Just because it’s Monday morning, why should we all dive right into the workweek? No, I vote for just a little more fun before kicking the productivity machine into high gear. What’s a little more fun? How about free Tetris clones for various platforms?
Windows and Linux: Try Cultris for single-player or multi-player. The multi-mode looks extremely challenging as players can send you "garbage lines" to hose you up.
Mac: Quinn came recommended by way of TUAW and quickly got me hooked. I didn’t like the default keyboard controls, but they were easy to adjust. This is another one with LAN / multiplayer support.
Windows Mobile: Kevtris is my pick. I’ll let you figure out why. ;)
Symbian: Take a quick peek at S-Tris 2 for your S60 or UIQ device.
iPhone: I see some projects for a Safari based version; here’s one to check.
Got a free Tetris clone to recommend for these or other platforms? Don’t leave any holes in the list: complete a row with a recommendation in the comments!