Strategic Edmund Zavada and James Whitehouse's Galactica has you move spaceships, overtake planets, control production, and wipe out your enemies, computer or networked, before they kill you.
Space is laid out randomly in two dimensions.
StarBound by Catfish Software is similar on a hexagonal grid, but for one player only. The new version for PowerPC is available in beta. Steven Taylor's Assassin is networkable and multi-player. On a grid with wall blocks, move, shoot, and try to second-guess your opponents 15 moves ahead as they do the same. The turns of all players then occur simultaneously.