Hedgewars is multiplatform, a free turn-based blast-em-up in the vein of Worms. It features a wide range of weapons, multiple maps, and excellent graphics and audio. Offers single player, multiplayer, and (in theory) multiplayer over the internet modes.
If you’ve ever wondered why there are so many Worm clones and offshoots here’s the reason: Worms is an extremely playable, fun game. Although there are many freeware Worms clones but many of these are DOS games that lag behind in their production qualities (and/or do not readily run on XP/Vista), which is why Hedgewars was such a fantastic find for me personally: it offers excellent graphics and sound and excellent playability and physics.
In contrast to Worms variations such as the brilliant Soldat (which abandoned the turn-based model in favor of real-time gameplay), Hedgewars is a very faithful adaptation that sticks to the turn-based model and recreates most of the original elements, from the wacky range of weaponry to the destructible environment, and even the cartoonish look and feel all the way down the little one-liners that the characters utter at the end of each turn.