Some time ago I helped Jeff Olson open source his wonderful 1990s roguelike Alphaman:

https://github.com/superjamie/alphaman-src

It's full of optimisations to keep the code small, such as QBasic calling into C routines, as Jeff also wanted the source to all fit on one floppy disk.

Fantastic! Now I'm off to check my source code files (in the author of the manifesto)