Colladv was an collaborative online textual game I made in 2014. It's one of the projects I was quite happy about.

The main interface was like a standard textual adventure game where you read descriptions of rooms and type sentences such as "open door" to interact.

But there was twist to it : each time a player typed an unknown commmand line, the game kept track of it.
If that command was the top unknown command for a given room (if many players had asked to do the same thing before) then the player could choose the consequences of the action by creating a new room or returning to a previous visited room.

The game started with only one room but due to an unexpected popularity rush, it expanded quickly and was filled by hundreds of rooms within a few hours (until my server crashed).

Here is a graph of possible interactions designed by players after a few hours :

I didn't include any item or player-wise variables, just descriptions of rooms. It seemed to be enough for players to have fun. I would still like to try a mud-like approach someday.

I made two versions of this game. The second version was slightly more stable and featured pictures but I decided to remove them at some point.

Due to technical reasons the game is buggy now but can still be played here Colladv.