I've got a lovely 3d adventure engine.
I doubt that it'd be much use to anyone else though, because you'd need to know a decent bit about programming for it to be useful. It's in a pretty advanced state; I'm always tinkering with the code/features. I've been working on it (on and off) for about a year and a half.
It uses real-time 3d backgrounds as opposed to 2d rendered backgrounds, unlike Grim Fandango or Raudaschl's tech demo. It also supports lots of groovy graphical effects. I'm not sure what I'm going to end up doing with it...