Pawn'd has gone free, the quite excellent Pawn'd.
It's a match three, basically, but with a chess theme. Each of the tiles can only move one space in the direction of the chess piece, so bishops can only move diagonally, etc. Pawns can only move forwards, but can move two spaces if you move them directly forward. Knights move like knights. With the right set-up, you can castle with a king and a rook. So yeah, it's match three but with a twist, and it works brilliantly.
There are a bunch of modes, too, some timed, some where you have time to think and plan ahead while meeting certain conditions, there's really something for everyone whether you like chess or not!