Enclosure is a twist on the classic Tower Defence genre in which you not only place guns, but also build walls and doors to keep the attackers at bay.
Enemies come from all sides and have several potential exit points, all of which must be protected using a combination of force fields and heavy weaponry.
The forcefields forms obstacles, to slow the attackers down long enough for the weapons to kill them, but they are a limited resource so you have to make the best use of them.
Each new turn adds more exit points, and thus, increases the strain on your available forcefield resource.
Enclosure was my second native Android App and was written entirely in Java using OpenGL for 3D rendering.