24 new celebration missions: https://www.ttlg.com/forums/forumdisplay.php?f=100&s=8913f3e040d4bf68d7da64224df5be84
For those who don't know Thief is a first person game where you try to not get spotted, hiding in shadows and blackjacking guards from back, looting places. The game takes place in a pseudo medieval steampunk world. The sound plays a big role in this game, as guards can hear your footsteps on hard surfaces.
Most people prefer Thief 2 because the original has super natural stuff like zombies, but for me Thief 2 was a huge disappointment, it didn't have the thick atmosphere and the level design was too plain.
There have been around one thousand fan missions and campaigns made in total in the last 20 years for Thief 1 and 2, also for Thief 3 and for the Dark Mod, but those are much less popular in the community.
I don't know any other fan community that has been so active for so long. For me it started in mid 2000s when Thief 2X: Shadows of the Metal Age was released, it was a big fan made campaign that took place between the timelines of Thief 1 and 2, after that I have been playing fan missions now and then, usually a few times a year. Admittedly most of them are weak, but there are some really good ones and masterpieces, I would say around 20% of all fan missions are worth your time, which is a lot considering how many have been made. The number would be much higher if so many mission authors wouldn't hide door keys, items and switches so much, or make obscure puzzles, grrr
I will later update with a list of my favorite fan missions.