I was heavily involved in various Nomic games (of that posted list, Agora and the Fantasy Rules Committee, and to some extent Internomic and I think Ackanomic as well; my site from grad school is one of the dead links under Agora) for a bunch of years during college and grad school, and it was deeply formative for me in terms of understanding how rules and systems work. And precise language. Agora was also the reason I learned Perl, when I got elected as the one who kept track of proposals and votes and inherited the perl scripts of my predecessor and had to read the man page (just one, it was Perl 4, excellently written but verrrry long) to learn the language to edit them. Which was also highly formative, come to think of it.

Agora still seems to be alive and well, though, and coming up on 30 years old, at agoranomic.org .