I've used it to run a campaign in single player.
Using Janitor AI, I setup a multi-personality AI using its D&D and games training presets and then fed it the SRD for 3.5 as well as all the stuff I wrote for my campaign and was able to play a game as a player all by myself because the AI handled being a DM and 3 other players.
It worked out pretty good. It didn't always understand the rules which lead to arguments... Just like it would with real people! 😃