Xena’s github page. This is where the things like my work in progress on M1F problem sheets is going.
Lean’s github page. This is where the source code for Lean is. Sometimes it’s worth reading, but to be honest I now realise that there are other ways of looking for what you need (for example VS Code’s auto complete functionality is a great way of looking for the function you want).
[Imperial College students only] Xena’s blackboard pages . Stuff that’s internal to Imperial goes here (for example times, dates, rooms of meetings etc). This link works for me but I run the pages. Someone let me know if this doesn’t work for Imperial students who are logged into blackboard.
Finally, for beginners, you could look at posts tagged learning-lean if you want an entry point.