A generic host based .NET core app which can be run as a Windows Service.
dotnet publish --configuration Release
sc create TaskBrokerService binPath= "c:\DATA\DEVELOP\TaskBrokerCore3\TaskBroker\bin\Release\netcoreapp2.2\win7-x64\publish\TaskBroker.exe"
sc start TaskBrokerService
For further details see the blog post Running a .NET Core Generic Host App as a Windows Service
External activation helps to execute external tasks (written in C#) from inside of Sql Server Stored Procedures. The benefits that the tasks (executors) are executed outside of Sql Server process and implemented in more robust language than Transact SQL. For example, i use it to write stored procedures for some Reports (in SQL Server Reporting Services) - when the report is executed the stored procedure triggers execution of a task and waits for its completion. When the execution of the task is completed, the report is created based on the data obtained from the execution of that task. There are more possibilities (Application to Application communication), but for them, it is more convenient to use other Message Buses (like - NServiceBus, MassTransit or Rebus). And this thing is better for SQL Server - Outside World communication (send emails, import data, etc). It can also be used as a relay to send mesages further to a different message broker like Kafka or Rabbit MQ.
It is difficult to plug SSSB transport into existing message buses, because SSSB message handling has its peculiar features which need special message processing infrastructure. So it is better to use specific application for this task, than to try to squeeze it into existing applications.