Stellar Survivor is a Sci-Fi FPS/Tower Defense hybrid where you mine crystals and build defenses to keep your powercore safe from waves of aliens.
In Stellar Survivor you are stranded on an alien planet and must defend the powercore which helps you survive from waves of alien attackers. You have access to an assault rifle, a shotgun and a sniper rifle, all of which have unlimited ammo but can require a little time to cool down if used too often.
You can also harvest crystals from crystal deposits and dead enemies which you can then use to build tower defense style defenses around your powercore. You can place turrets, spike traps, electric towers, mines and barriers, allowing you to kill enemies and to alter the routes the aliens take to your powercore.
At the moment the variety of units and depth of the tower defense elements are a little underwhelming, but the first person combat is great. You can quickly become overwhelmed with alien forces when playing on your own, but the devs are planning to add multiplayer co-op which should help to balance things out a little. It shows a lot of promise and should make for a great co-op bit of alien blasting tower defense FPS fun.