Tower defense started as a popular modification to Blizzard's Warcraft III. The gameplay--building and upgrading various towers that shoot at ever-stronger lines of enemies marching toward the player's base--proved addictive enough to pave way for the PlayStation 3 release of Q-Games's PixelJunk Monsters and an expansion pack earlier this year.

With Defense Grid, Hidden Path is bringing the tower-defending phenomenon back to its PC roots with 20 levels. The game will be released this November.