Gyra is a game about defending your energy core from enemies.
Press Up (or W) to grow the core. The core spins faster if you grow it more, but also makes it more vulnerable to enemies. More points are awarded if the core is larger.
Press Down (or S) to shrink the core.
Press Escape to go back or quit the game.
You can read reviews of the Ludum Dare version here.
The web version was exported with Unity 5.2 HTML5 exporter. If something isn’t working there, I highly recommend that you try out a desktop version of the game. Gyra is also available on the App Store for both iPhone and iPad.