Various efforts, some dating back to 1980's and 1990's research papers etc.
Any specific licences will be displayed within the relevant sub-directories.
Some of this stuff may build (and work). Some may not. Don't look here for active work.
Anything that builds will have a mention in its README.md. Lack of a mention doesn't necessarily indicate it won't build but there's a good chance that is the case. However, to try to provide more help, if something definitely doesn't build I'll try to call that out in the README.md too.