In April 2023 I have decided to split nissy in 2 separate projects: an optimal solver and an FMC assistant. These two projects are not usable yet, so in the meantime I will keep a third branch where I update the classic version of nissy with bugfixes and minor improvements.
You can find these three branches at the following pages (also on github, links below are to my personal git instance):
If you are happy with using nissy as it is, you can keep using it.
When nissy-fmc and nissy-classic are ready, you can chek them out too.
Then I encourage you to keep using nissy-classic :-)
See my blog post for some reasons behind this change.
If you want to check out the git repository of the version you are running, you probably want nissy-classic. The newer nissy-fmc will eventually be nicer and easier to read, containing more or less the same functionality (except for optimal solving).
If you want to follow my progress on an advanced optimal Rubik's cube solver, you can check out nissy-nx - just remember that it does not work yet!