I've recently been playing the free version of AI Dungeon. It's a text-based game which attempts to replicate the flexibility of a tabletop game by using GPT-2 as an automated GM. I've only been playing it in single-player mode, though it does have multiplayer.

Currently, the AI isn't anywhere near as good as a human GM, and it frequently does nonsensical things, but it's somewhat fun to spend a little time on.