Have you tried collaborating with Forth? There's a lot of documented history of people doing so in industry when it was actually used, and more recently I've usually found Forth codebases approachable and easy to follow.

Personally I think this is the pay-off for writing the code in the first place because Forth is very difficult to write in a clear way, if you actually manage to do it you've probably made it very clear to follow because otherwise it's hard to finish your project and make it work at all.