In last five years I have made a bunch of forum games. Maybe I will give a short description of each of the more successful ones?
Era of Diesel: Ever heard of Diplomacy board game? Did you hear of Master of Orion series? I mixed those two so you have 1900-era Diplomacy with nation management, research, and other such things.
Squire: Commodore 64 look-alike text adventure. I basically input text into C64 stylized panels. The game is about 15-years old squire who is now out into the world and hopefully not die from court politics, warfare, poverty, diseases and other such things in low-magic fantasy world.
SpaceXplorers!: A fast-paced board-like game where 4 players roam the board, fighting aliens, exploring ancient ruins, mining minerals on planets and trading with other spaceships to acquire 5000 credits and win the race.
Medieval Fodder: A big two-team deathmatch depicting one battle in randomly made up fantasy world. Some of the playthroughs had up to 50 players involved!
There's also Fire Emblem on Forums, aka FEF, but it's too much for this little forum.
Would any of such games above catch interest amongst SSSS forumites?