This was developed as part of the RuneScape Wiki maps project.
You cna contribute by searching for old game caches
You can clone the repository and use it locally. Most of the data used is located in git submodules. As such you need to initialize those as well. You can do that with:
git clone --recurse-submodules https://github.com/mejrs/mejrs.github.io.git
Note that you can not simply open this in your browser - you need to set up a local HTTP server to run it.
The data in this repository can be generated using https://github.com/mejrs/rs3cache/. For more information on how the maptiles are built, see this document.