rdlu
From the "I wanted it to exist so I made it" department, I present: rdlu. It's a Sokoban clone. But you can create and share levels on Secure Scuttlebutt. The levels also contain full cellular automata-style rules for the game (@$_ => _@*), so you can modify and add to those, too. Finally, I made it in Tilde Friends, so you can muck with the source as much as you like and make it into your own thing entirely.
It publishes and consumes rdlu-level messages with a source field containing a description of the level and rules as text.
If you just want to see it in action, it lives here, no Tilde Friends account required to play: https://www.tildefriends.net/~cory/rdlu/.
image:rdlu, a puzzle game with a person pushing boxes like Sokoban