Described here. Location aware seems to be the main differentiator from other similar apps (like the UK Liftshare). I think that could be useful sometimes, and not other times – if I am planning my return trip from somewhere, then having the app be aware of where I am now isn’t all that useful.
Both Liftshare and Carticipate are also Facebook apps, which seems to be the way the world is going. As with the web n years ago, if you are not on Facebook you don’t exist. Sad but true.