Gratuitous Tank Battles is the latest PC strategy game from Positech Games. www.gratuitoustankbattles.com. GTB is a unique blend of Strategy, RTS, Management and Tower-defense. You can play every battle from either the attacker or defender POV, with three different difficulty levels against both a scripted or an adaptive AI. You can even save out your attack and play against it as defender.
In addition, the game also uses customised-units you build yourself from scratch, for endless variety, plus a built-in level editor which allows you to trivially alter a map or create new ones from scratch.
Not only that, but the game also supports an online challenge and map-sharing system that lets you share, download, rate, comment-on and play maps and armies designed by other GTB players.