Playtested the "Motive and Opportunity" mini-game on the Foundry.  Here's the log if people want the blow-by-blow.

The game is almost entirely mechanics free, but nicely structured.  There's a murder.  One person explains why their character wouldn't have done it (cue the strains of "My Guy would never do that!") and then the person to their right explains why that character totally would have done the deed.  The new person then explains why their character has no motive, and the person to their right debunks that, and so on around the circle.

Then the first person debunks the last person's motive and goes on to explain how their character had no opportunity to do the crime ("My Guy couldn't do that!").  The order around the circle reverses, so the person on their left debunks their alibi (or disability, or whatever) and posits their own.

And that's the game.  In play it was a great deal of fun ... people thought up some wild motives for each other.  I still think my favorite was when Lxndr, on the first turn, immediately posited that my character (Lady Dunham) found his character (Lord Stanhope) in bed with her husband and vowed bloody revenge.  On one level, it's no better than claiming that Dunham was in bed with the butler ... the shameful adultery is just as good a motive whoever it is.  On another level though, the fact that Lxndr so totally involved his character made it a much more telling shot.  There's something there about how making yourself vulnerable gives you social power, but I'm not having good luck fishing it up out of my murky semi-consciousness.

Jasper commented, after the game, that part of the fun was that the players have no chance to defend themselves.  You just put your character out there, and know that they're going to be slammed.  But to the extent that your goal is to look like the least likely suspect, the only way to defend yourself is by slamming someone else in such a way that everyone thinks they're the murderer.

I don't know whether that's really the point of the game, though.  People were a lot more interested in just developing the wildly perverted and dysfunctional family in which they murder occurred than they were in pinning the murder on anyone.  That whole stage of end-game may be unnecessary.

To leap feet-first into the quagmire:

The secret of this game's success strikes me as the great "I pull to get you to push" dynamic it sets up. My description of why My Guy wouldn't have/couldn't have/wasn't there/had a manicurist's appointment at the time is understood, unambiguously, by everyone involved as something I've just put out there for everyone else to trample gleefully. Just as Prime Time Adventures works less by the formal mechanics than by enabling a collaborative-brainstorming mindset, this game works by enabling ("giving permission," in a sense) a dynamic of "sure, you can screw with me -- in fact, I'll make it easy! -- now top that!" It's the Turtle Killer.