There are few games quite as relaxing to play as Mahjong solitaire. Moonlight Mahjong is a great free solitaire game for the Mac, that's tuned for using a trackpad.
Not to be confused with classic game of mahjong, Mahjong solitaire is a tile matching game where you're presented with a pile of tiles taken from mahjong (hence the name), with the task of matching pairs to whittle down the pile. The tiles are stacked on top of each other, making only a limited number available for matching at any one time.
Moonlight Mahjong gives you the choice of four different playing modes: Scramble and Challenge modes, where you compete against the computer, aka "Tilebot" to clear the board; Puzzle, which is classic mahjong solitaire without Tilebot; and finally Relaxation, which is like Puzzle mode but there are no time limits and your tiles are automatically reshuffled.
The 3D tiles give you a bit of depth perception, while the pile is displayed atop one of its gorgeous backgrounds. You've got the choice of some beautiful Hubble images, paintings or photos, while the sound effects have a wind-chime style to them. Having come from iOS, the developers have given the game a touch-like feel by implementing decent multi-touch trackpad controls. You can select a tile by just lifting your finger off the trackpad, while you can move the pile about with standard gestures (pinch-to-zoom etc).
Moonlight Mahjong looks great, plays well and adds a little competitive element with the introduction of your Tilebot playing partner. If you're looking for a relaxing game for your Mac and like matching tiles, the free Moonlight Mahjong is definitely worth a look.