I suggest doing the UTT challenge in two parts:

1. On the first "weekend-challenge", design the game (and choose a winning design)
2. For the next "weekend-challenge", implement the game (matching the design/requirements decided on the first phase of the challenge)

Benefits:

- More like real-life (design before code)
- Inter-operable implementations from the second phase of the challenge (because they use the same high-level design)

I suggest the following requirements for the design:

- Program I/O and UI must support two interactive players over a network: human versus human, human versus bot, or bot versus bot.
- Game state must be presented (to the I/O i.e. UI) in a human-readable and machine-readable format.
- Game rules won't change in the future (you can optimize or specialize your design for UTT only, and needn't make it generalizable for other games)

Essentially, the first challenge is to specify the program's I/O, i.e. its interface to the outside word and users.

If you believe in Test Driven Development, it should be possible to write one or more bots which use the I/O to play the game, before the game itself is written to implement that I/O.

Expected answers will define/specify the I/O and/or UI. They should be clear enough that bots can be written using that specification and will then interoperate with game implementations.

You might argue that 'design' instead of 'code' is off-topic for this site, but I'd argue that:

- I'm looking for an unambiguous specification (which, is similar to code)
- You can optionally include code for a bot which plays the game (however badly) using that specification