Icehouse

Icehouse

Designers: John Cooper and Andrew Looney
Type: Icehouse
Status: Free
BGG entry: http://www.boardgamegeek.com/game/225
Available at: http://www.wunderland.com/icehouse/IcehouseRules.html

From the BGG entry:

This bizarre little game completely does away with the concepts of turn sequence and structure, as it doesn't use turns, or rounds, or anything else to break up the action. Players place their pieces as quickly or slowly as they like, in attacking or defending positions. Only when everyone's used up all their pieces is the game scored, with people getting points for their safe defenders and successful attackers.

From the IcehouseGames Wiki:

Icehouse, the original game to play with your elongated pyramids, was envisioned by Andrew 'The Emperor' Looney as part of his Empty City series of stories and turned into a game by John 'Dr. Cool' Cooper. It is a real-time game of attack and defense, played on any flat surface.

It's not a perfect game, but it has a dedicated fan base who really enjoy its combination of strategy, tactics, and diplomacy.