One nice addition to achievements: when it is based on a single game, include a link to the game with the achievement. I just got an achievement for rolling all six types of doubles in a backgammon game, but there was no obvious way to go back and look at the game.

I've thought of a new backgammon variant (or at least one that I haven't heard about before). Crowded Antibackgammon. The initial board setup is like Crowded Backgammon, as are the rules of movement. Winning conditions are as in Antibackgammon: force your opponent to bear off first. I know at least one other person who's quite excited about the possibility, and it's probably simple to implement.

Does the concept interest other people too?