diff --git a/app/channels/application_cable/connection.rb b/app/channels/application_cable/connection.rb
index 251cbd8..8e8a8b7 100644
--- a/app/channels/application_cable/connection.rb
+++ b/app/channels/application_cable/connection.rb
@@ -11,7 +11,7 @@ def connect
     protected
 
     def find_verified_user
-      if verified_user = env['warden'].user
+      if (verified_user = env['warden'].user)
         verified_user
       else
         reject_unauthorized_connection
diff --git a/app/controllers/users_controller.rb b/app/controllers/users_controller.rb
index 3b9390c..3431203 100644
--- a/app/controllers/users_controller.rb
+++ b/app/controllers/users_controller.rb
@@ -1,6 +1,6 @@
 class UsersController < ApplicationController
   def show
-    @user = User.find(params[:id])
+    @user = params[:id].to_i == -1 ? System.new : User.find(params[:id])
   end
 
   def index
diff --git a/app/models/activity.rb b/app/models/activity.rb
index 55147d6..5bcce28 100644
--- a/app/models/activity.rb
+++ b/app/models/activity.rb
@@ -13,6 +13,54 @@ class Activity
     vote.create
   ].freeze
 
+  # outer key: defines the key of an activity ('.' replaced with '_')
+  #   => this way each key can cache different data
+  # inner key: caching_key
+  # inner value: method(s) to call on an activity (via send) to get the cache value
+  CACHE_CONFIG = {
+    app_create: {
+      app_name: 'trackable.name',
+      user_username: 'owner.username'
+    },
+    comment_create: {
+      comment_content: 'trackable.content',
+      user_username: 'owner.username',
+      stampable_name: 'recipient.stampable_name'
+    },
+    domain_create: {
+      domain_name: 'trackable.name',
+      user_username: 'owner.username'
+    },
+    stamp_accept: {
+      stampable_name: 'trackable.stampable_name',
+      stampable_type: 'trackable.type'
+    },
+    stamp_archive: {
+      stampable_name: 'trackable.stampable_name',
+      stampable_type: 'trackable.type'
+    },
+    stamp_create: {
+      stampable_name: 'trackable.stampable_name',
+      stampable_type: 'trackable.type'
+    },
+    stamp_deny: {
+      stampable_name: 'trackable.stampable_name',
+      stampable_type: 'trackable.type'
+    },
+    stamp_dispute: {
+      stampable_name: 'trackable.stampable_name',
+      stampable_type: 'trackable.type'
+    },
+    user_signup: {
+      user_username: 'trackable.username'
+    },
+    vote_create: {
+      user_username: 'owner.username',
+      stampable_name: 'recipient.stampable_name',
+      stampable_type: 'recipient.type'
+    }
+  }.freeze
+
   def persisted?
     false
   end
diff --git a/app/models/comment.rb b/app/models/comment.rb
index ce6283c..23ee2b4 100644
--- a/app/models/comment.rb
+++ b/app/models/comment.rb
@@ -1,6 +1,9 @@
 class Comment < ApplicationRecord
   include PublicActivity::Common
 
+  # :commentable can currently only be used with stamps
+  # comment.create activities caches data of stamps, so this would fail if used on another object
+  # in cache config => comment_create => stampable_name is cached
   belongs_to :commentable, polymorphic: true
   belongs_to :user
 
diff --git a/app/models/concerns/votable/state.rb b/app/models/concerns/votable/state.rb
index 8c50e90..fe831c2 100644
--- a/app/models/concerns/votable/state.rb
+++ b/app/models/concerns/votable/state.rb
@@ -2,6 +2,7 @@ module Votable
   module State
     extend ActiveSupport::Concern
 
+    # rubocop:disable Metrics/BlockLength
     included do
       # used so boosts can reference the transition_activity
       attr_accessor :transition_activity
@@ -54,6 +55,7 @@ module State
         end
       end
     end
+    # rubocop:enable Metrics/BlockLength
 
     def scheduled_at
       created_at + ENVProxy.required_integer('STAMP_CONCLUDE_IN_HOURS').hours
diff --git a/app/models/notification.rb b/app/models/notification.rb
index 64297e0..6e08b45 100644
--- a/app/models/notification.rb
+++ b/app/models/notification.rb
@@ -4,7 +4,7 @@ class Notification < ApplicationRecord
   belongs_to :recipient, class_name: 'User'
   belongs_to :reference, polymorphic: true
 
-  after_create { NotificationBroadcastWorker.perform_async(self.id) }
+  after_create { NotificationBroadcastWorker.perform_async(id) }
 
   validates_presence_of %i[activity actor recipient reference]
 
diff --git a/app/models/stamp.rb b/app/models/stamp.rb
index e3675ec..5ca84c4 100644
--- a/app/models/stamp.rb
+++ b/app/models/stamp.rb
@@ -27,7 +27,12 @@ def peers?
   end
 
   # must be implemented @ each subclass
-  # can describe a stronger connection than peers
+  #   -> used to describe the stampable object in the UI
+  def stampable_name
+    raise NotImplementedError
+  end
+
+  #   -> can describe a stronger connection than peers
   def siblings
     raise NotImplementedError
   end
diff --git a/app/models/stamp/flag.rb b/app/models/stamp/flag.rb
index f63862c..82e3daa 100644
--- a/app/models/stamp/flag.rb
+++ b/app/models/stamp/flag.rb
@@ -12,6 +12,10 @@ def app
     stampable
   end
 
+  def stampable_name
+    app.name
+  end
+
   def siblings
     peers
   end
diff --git a/app/models/stamp/label.rb b/app/models/stamp/label.rb
index de44d08..f76fc94 100644
--- a/app/models/stamp/label.rb
+++ b/app/models/stamp/label.rb
@@ -14,6 +14,10 @@ def domain
     stampable
   end
 
+  def stampable_name
+    domain.name
+  end
+
   def initial_stamp_cannot_be_0
     return true if percentage != 0
     return true if siblings.accepted.present?
diff --git a/app/models/system.rb b/app/models/system.rb
index 3e2337b..4c907ce 100644
--- a/app/models/system.rb
+++ b/app/models/system.rb
@@ -9,4 +9,12 @@ class System < User
   def self.polymorphic_name
     'System'
   end
+
+  def created_at
+    '01-01-2019'.to_date
+  end
+
+  def updated_at
+    created_at
+  end
 end
diff --git a/app/views/activities/_comment.create.html.haml b/app/views/activities/_comment.create.html.haml
index 2855de0..2e35841 100644
--- a/app/views/activities/_comment.create.html.haml
+++ b/app/views/activities/_comment.create.html.haml
@@ -1,4 +1,4 @@
 commented on a
 = link_to activity.recipient_type, activity.recipient
 of
-= link_to activity.recipient.stampable.name, activity.recipient.stampable
+= link_to activity.recipient.stampable_name, activity.recipient.stampable
diff --git a/app/views/activities/_vote.create.html.haml b/app/views/activities/_vote.create.html.haml
index 5782d3c..89b68ba 100644
--- a/app/views/activities/_vote.create.html.haml
+++ b/app/views/activities/_vote.create.html.haml
@@ -1,6 +1,6 @@
 voted for a
 = link_to activity.recipient_type, activity.recipient
 of
-= link_to activity.recipient.stampable.name, activity.recipient.stampable
+= link_to activity.recipient.stampable_name, activity.recipient.stampable
 its
 = activity.recipient.state
diff --git a/app/views/notifications/_notification.html.haml b/app/views/notifications/_notification.html.haml
index 7973b7a..1fd623c 100644
--- a/app/views/notifications/_notification.html.haml
+++ b/app/views/notifications/_notification.html.haml
@@ -6,4 +6,4 @@
     = render partial: "notifications/#{notification.activity.key}", locals: { notification: notification }
     = link_to notification.reference_type, notification.reference
     of
-    = link_to notification.reference.stampable.name, notification.reference.stampable
+    = link_to notification.reference.stampable_name, notification.reference.stampable
diff --git a/cable/config.ru b/cable/config.ru
index 341e724..e049ff1 100644
--- a/cable/config.ru
+++ b/cable/config.ru
@@ -1,4 +1,4 @@
-require ::File.expand_path('../../config/environment',  __FILE__)
+require ::File.expand_path('../../config/environment', __FILE__)
 Rails.application.eager_load!
 
 run ActionCable.server
diff --git a/config/initializers/public_activity.rb b/config/initializers/public_activity.rb
index ce00be5..0ea5abc 100644
--- a/config/initializers/public_activity.rb
+++ b/config/initializers/public_activity.rb
@@ -3,4 +3,41 @@
   has_many :boosts, foreign_key: :trigger_id # a trigger can cause multiple boosts, iE stamp.accept
 
   validates :key, presence: true, inclusion: { in: Activity::KEYS }
+
+  # key can only have one dot (.) as defined in Activity::KEYS
+  def config_key
+    key.sub('.', '_').to_sym
+  end
+
+  # if it is not set yet, it will fetch and set the data
+  # second call already retrieves the cache
+  # => adding caches in Activity::CACHE_CONFIG is no big deal & performant
+  def cache(cache_key)
+    value = parameters[cache_key.to_s]
+
+    return value if value.present? || !cache_key_set?(cache_key)
+
+    set_cache!
+    cache(cache_key)
+  end
+
+  def cache_key_set?(cache_key)
+    Activity::CACHE_CONFIG[config_key][cache_key.to_sym].present?
+  end
+
+  # if you want to reload all of the caches, use PublicActivity::Activity.all.each(&:set_cache!)
+  # though it is still performant to just get the caches whenever needed
+  def set_cache!
+    Activity::CACHE_CONFIG[config_key]&.each do |cache_key, retrievers|
+      parameters[cache_key.to_s] = fetch_value(retrievers)
+    end
+
+    save if changed?
+  end
+
+  def fetch_value(retrievers)
+    retrievers.split('.').inject(self) do |cache_value, retriever|
+      cache_value.send(retriever)
+    end
+  end
 end
diff --git a/spec/factories/activity.rb b/spec/factories/activity.rb
index 2035f7b..91cc922 100644
--- a/spec/factories/activity.rb
+++ b/spec/factories/activity.rb
@@ -3,18 +3,22 @@
     association :owner, factory: :user
   end
 
-  factory :domain_activity, parent: :activity do
-    association :trackable, factory: :domain
-
-    key { 'domain.create' }
-  end
-
   factory :app_activity, parent: :activity do
     association :trackable, factory: :app
-
     key { 'app.create' }
   end
 
+  factory :comment_activity, parent: :activity do
+    association :trackable, factory: :comment
+    recipient { trackable.commentable }
+    key { 'comment.create' }
+  end
+
+  factory :domain_activity, parent: :activity do
+    association :trackable, factory: :domain
+    key { 'domain.create' }
+  end
+
   factory :signup_activity, parent: :activity do
     association :trackable, factory: :user
     key { 'user.signup' }
@@ -34,6 +38,13 @@
     key { 'stamp.accept' }
   end
 
+  factory :user_activity, parent: :activity do
+    association :trackable, factory: :user
+    owner { trackable }
+    recipient { nil }
+    key { 'user.create' }
+  end
+
   factory :vote_activity, parent: :activity do
     transient do
       vote { create(:vote) }
diff --git a/spec/factories/comments.rb b/spec/factories/comments.rb
index 7fbf122..a2d1395 100644
--- a/spec/factories/comments.rb
+++ b/spec/factories/comments.rb
@@ -6,7 +6,7 @@
     association :commentable, factory: :label_stamp
   end
 
-  # meaning: the comment & commentable were created by the same user 
+  # meaning: the comment & commentable were created by the same user
   factory :initial_comment, parent: :comment do
     commentable { create(:label_stamp, creator: user) }
   end
diff --git a/spec/factories/stamps.rb b/spec/factories/stamps.rb
index 2ee4b95..51b8298 100644
--- a/spec/factories/stamps.rb
+++ b/spec/factories/stamps.rb
@@ -26,7 +26,7 @@
     end
 
     trait :with_comments do
-      after(:create) do |stamp, evaluator|
+      after(:create) do |stamp, _|
         stamp.comments << FactoryBot.build(:comment, commentable: stamp, user_id: stamp.user_id)
         stamp.comments << FactoryBot.build_list(:comment, 2, commentable: stamp)
         stamp.save
diff --git a/spec/models/activities_spec.rb b/spec/models/activities_spec.rb
deleted file mode 100644
index 65a323e..0000000
--- a/spec/models/activities_spec.rb
+++ /dev/null
@@ -1,25 +0,0 @@
-RSpec.describe PublicActivity::Activity, type: :model do
-  describe 'relations' do
-    it { is_expected.to have_one(:boost).with_foreign_key(:cause_id) }
-    it { is_expected.to have_many(:boosts).with_foreign_key(:trigger_id) }
-  end
-
-  describe 'database' do
-    it { is_expected.to have_db_index(%i[trackable_id trackable_type]) }
-    it { is_expected.to have_db_index(%i[owner_id owner_type]) }
-    it { is_expected.to have_db_index(%i[recipient_id recipient_type]) }
-  end
-
-  describe 'validations' do
-    it { is_expected.to validate_presence_of(:key) }
-    it { is_expected.to validate_inclusion_of(:key).in_array(Activity::KEYS) }
-  end
-
-  describe 'view partials' do
-    Activity::KEYS.each do |key|
-      it "#{key}.html.haml partial exists" do
-        expect(File).to exist("app/views/activities/_#{key}.html.haml")
-      end
-    end
-  end
-end
diff --git a/spec/models/activity_spec.rb b/spec/models/activity_spec.rb
new file mode 100644
index 0000000..b03072f
--- /dev/null
+++ b/spec/models/activity_spec.rb
@@ -0,0 +1,131 @@
+RSpec.describe PublicActivity::Activity, type: :model do
+  describe 'relations' do
+    it { is_expected.to have_one(:boost).with_foreign_key(:cause_id) }
+    it { is_expected.to have_many(:boosts).with_foreign_key(:trigger_id) }
+  end
+
+  describe 'database' do
+    it { is_expected.to have_db_index(%i[trackable_id trackable_type]) }
+    it { is_expected.to have_db_index(%i[owner_id owner_type]) }
+    it { is_expected.to have_db_index(%i[recipient_id recipient_type]) }
+  end
+
+  describe 'validations' do
+    it { is_expected.to validate_presence_of(:key) }
+    it { is_expected.to validate_inclusion_of(:key).in_array(Activity::KEYS) }
+  end
+
+  describe '#config_key' do
+    subject { activity.config_key }
+    let(:activity) { FactoryBot.create(:signup_activity) }
+
+    it 'replaces the key´s . with _' do
+      expect(subject).to eq(:user_signup)
+    end
+
+    it 'returns a symbol' do
+      expect(subject.class).to eq(Symbol)
+    end
+  end
+
+  describe '#cache_key_set?(cache_key)' do
+    subject { activity.cache_key_set?(cache_key) }
+    let(:activity) { FactoryBot.create(:app_activity) }
+
+    context 'cache_key is configured' do
+      let(:cache_key) { :app_name }
+
+      it 'returns true' do
+        expect(subject).to be true
+      end
+    end
+
+    context 'cache_key is not configured' do
+      let(:cache_key) { :unset_key }
+
+      it 'returns false' do
+        expect(subject).to be false
+      end
+    end
+  end
+
+  describe '#cache(cache_key)' do
+    subject { activity.cache(cache_key) }
+
+    let(:activity) { FactoryBot.create(:signup_activity, parameters: parameters, trackable: user) }
+    let(:user) { FactoryBot.create(:user) }
+    let(:parameters) { {} }
+
+    context 'cache_key is set' do
+      let(:cache_key) { :user_username }
+
+      context 'cache is already set' do
+        let(:parameters) { { user_username: user.username } }
+
+        it 'returns the cached value' do
+          expect(subject).to eq(user.username)
+        end
+      end
+
+      context 'cache is not set yet' do
+        it 'sets the cache' do
+          expect { subject }.to change { activity.parameters }.from({}).to(
+            'user_username' => user.username
+          )
+        end
+
+        it 'recalls #cache(cache_key) to return the value' do
+          expect(activity).to receive(:cache).twice.with(cache_key).and_call_original
+          subject
+        end
+      end
+    end
+
+    context 'cache_key is not set' do
+      let(:cache_key) { :unset_key }
+
+      it 'returns nil' do
+        expect(subject).to eq nil
+      end
+    end
+  end
+
+  describe '#fetch_value(retrievers)' do
+    subject { activity.fetch_value(retrievers) }
+
+    describe 'CACHE_CONFIG' do
+      Activity::CACHE_CONFIG.each do |config_key, config_hash|
+        model_type = config_key.to_s.split('_').first
+        factory_key = "#{model_type}_activity".to_sym
+        activity_key = config_key.to_s.sub('_', '.')
+
+        context "for '#{activity_key}' activity" do
+          config_hash.each do |cache_key, retrievers|
+            let(:activity) { FactoryBot.create(factory_key, key: activity_key) }
+            let(:retrievers) { retrievers }
+
+            describe "cache_key: #{cache_key}" do
+              describe "#fetch_value('#{retrievers}')" do
+                it 'does not raise an error' do
+                  expect { subject }.not_to raise_error
+                end
+
+                it 'does not return nil' do
+                  expect(subject).not_to eq(nil)
+                end
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+
+  describe 'view partials' do
+    Activity::KEYS.each do |key|
+      it "#{key}.html.haml partial exists" do
+        expect(File).to exist("app/views/activities/_#{key}.html.haml")
+      end
+    end
+  end
+end
diff --git a/spec/models/comment_spec.rb b/spec/models/comment_spec.rb
index e9e4e4e..5246f85 100644
--- a/spec/models/comment_spec.rb
+++ b/spec/models/comment_spec.rb
@@ -60,7 +60,9 @@
         expect { subject }.to change { Notification.count }.by(2)
       end
 
+      # rubocop:disable LineLength
       it 'creates notifications {activity: self, actor: actor, recipient: other commenters, reference: stamp}' do
+        # rubocop:enable LineLength
         subject
 
         activity = PublicActivity::Activity.last
diff --git a/spec/models/notification_spec.rb b/spec/models/notification_spec.rb
index 1744f39..752d289 100644
--- a/spec/models/notification_spec.rb
+++ b/spec/models/notification_spec.rb
@@ -21,7 +21,7 @@
     it { is_expected.to have_db_index(:activity_id) }
     it { is_expected.to have_db_index(:actor_id) }
     it { is_expected.to have_db_index(:recipient_id) }
-    it { is_expected.to have_db_index([:reference_type, :reference_id]) }
+    it { is_expected.to have_db_index(%i[reference_type reference_id]) }
   end
 
   describe '#create' do
@@ -37,7 +37,7 @@
     subject { notification.actor }
 
     context 'actor_id is -1' do
-        let(:notification) { FactoryBot.create(:notification, :system_actor) }
+      let(:notification) { FactoryBot.create(:notification, :system_actor) }
 
       it 'returns the System object' do
         expect(subject).to eq(System.new)
diff --git a/spec/views/semantic/header.html.haml_spec.rb b/spec/views/semantic/header.html.haml_spec.rb
index b3458f9..af7c6f1 100644
--- a/spec/views/semantic/header.html.haml_spec.rb
+++ b/spec/views/semantic/header.html.haml_spec.rb
@@ -13,7 +13,6 @@ def rendered
     context 'user has notifications' do
       let(:user) { FactoryBot.create(:user, :with_notifications) }
 
-
       it 'shows the notification inbox as a purple icon' do
         expect(rendered).to have_css('.inbox.purple.large.icon')
       end
diff --git a/spec/workers/notification_broadcast_worker_spec.rb b/spec/workers/notification_broadcast_worker_spec.rb
index 4e2a908..ca2bd97 100644
--- a/spec/workers/notification_broadcast_worker_spec.rb
+++ b/spec/workers/notification_broadcast_worker_spec.rb
@@ -2,7 +2,7 @@
   describe '#perform' do
     subject { worker.perform(notification.id) }
 
-    let(:worker) { NotificationBroadcastWorker.new() }
+    let(:worker) { NotificationBroadcastWorker.new }
     let(:notification) { FactoryBot.create(:notification) }
 
     it 'calls NotificationsChannel.broadcast_to' do