And I was expecting an article about Dungeon Crawl. Blows everything else out of the water for many years now.
Also playable by ssh.
DCSS is a remarkable open source project. The game's design is focused and coherent, avoiding "feature creep". Yet the devs are open to community suggestions and stay on good terms with the players. I can't think of any other project that so well harnesses the creativity of random internet people.
it's an ASCII rogue-like, not a text-only game. You could say it's a character only game. ;)