If.cruels.net
From IFWiki
if.cruels.net is a website where you can play a Z-code game using the Parchment interpreter, allowing multiple players to share a play session. All players can enter game commands at any time. Each command is preceded by the nick of the player who entered the command.
Limitations
- Only games that are available at the Interactive Fiction Archive can be played.
- There is no way to start a play session where only invited people get access.
- If you quit the game, the session is dead.