DriveThruRPG
www.drivethrurpg.com
I like the look of this, the notion of employing players tendencies to take the thinnest even imaginary 'connections' and run with with really seems promising for a light hearted pick up game. And I've got a ton of random tables (partially due to my hopefully soon to be started solo gaming experiment) so that would help keep things interesting.
I am wondering what the system being sold adds to the experience as it seems like you could do this with any system you're comfortable with improvising with.