Another pretty cool freebie has just hit the App Store, and this one’s a first-timer. Sentinel 4: Dark Star ($0.99), the latest in Origin8’s long-running series of tower defense games. This is a big and busy tower defense game, with levels so massive that they won’t even fit on one iPad screen. The game is somewhat of a hybrid between both fixed- and open-path tower defense games, as you have paths to place towers along, but can also deploy units in the paths in order to help defeat the oncoming hordes.

While the game does use a two-tier currency system with in-app purchases, you are getting a formerly-$4.99 game for free here. The freebie is planned to last until Monday, so get on this one while you can. Previous Sentinel games only go free every so often, so you might not get another chance to pick this up for a while. This is a rather deep tower defense game, and a good-looking one, to boot.