There is no official Tetris game for Mac but Tetris Zone is about as close as it gets.
Tetris Zone is a very accurate Tetris clone that offers four modes of play from a simple Challenge mode to a super fast Master mode. Tetris Zone accurately recreates the same 3D graphics and gameplay that makes Tetris so addictive. Note that this is a free demo for Macs, but the trial game limits your play and available feature set.
Specifically, there are four modes:
Marathon: How long can you last? (The closest thing to normal Tetris with 15 levels)
Challenge: Tests how far you can go in 10 minutes
Sprint: A race to clear 40 lines as fast as possible
Master: Super fast drops requires super fast thinking!
Beyond this, it doesn't offer any new innovations on the Tetris genre but it does give you full instant replays plus it stores your all-time and daily best scores. Your best scores are automatically uploaded to the worldwide Leader Board so you can compare yourself with the best in the World.
Tetris Zone is the closest thing to an official free demo of Tetris on Mac.