Hi folks,
I've always been interested in inductive reasoning games, where you have to guess an overall pattern from examples.
The most prominent games here are Eleusis and Zendo. Both have a games master (god, master) think of a secret rule. All other players (scientists, students) carry out experiments, which are marked by the master as conforming to the rule or not. Th scientists's main task is to guess the secret rule governing this marking.
In
Eleusis, players take turns adding playing cards to a central sequence.
Here's a writeup of how I've played it. The secret rule governs which cards fit onto the end of the current sequence. Invalid plays are placed to the side of the current sequence's end, to remind people later on that this card didn't conform to the rule at that point.
Scientists win if they empty their hand of cards first, and must draw replacement cards for invalid plays. If someone feels pretty sure about the secret rule, he can declare himself prophet and judge other people's plays before the god does. Judging correctly allows the prophedt to discard additional cards from hand, but judging incorrectly leads to a severe penalty of extra hand cards.
In
Zendo, as described on the
excellent Zendo website by its designer, no sequence is built. Instead, predefined building blocks (Icehouse pieces) are arranged in various manners, each such arrangement is called a koan. The master marks koans as conforming to the rule or as not. There is no penalty for testing nonconforming koans. The goal is to formulate a rule that is equivalent to the master's rule, i.e., the master cannot build a counterexample that satisfies only either the guessd rule or the master's rule.
Would people be interested in this as a forum game? Unless tons of people discourage me from this, I'm going to start a forum game thread soon.

An alternative is to play on IRC.
What might be the best forum game rules? One standard method on the net seems to play Zendo with words, i.e., arbitrary strings of characters [A-Z]. Customly made Lemmings levels are also possible, but too unwieldy to build in large quantities for a forum game. ;-)
I'd play without turns, so everybody can simply post test cases for the master to mark, and guess rules, which can lead to a win or a counterexample. Testing cases should be free of penalty (0 points), or almost free (-1 point). A false guess should only bring about a minor penalty (-10 points) compared to guessing the correct rule (+100 points or something).
-- Simon