PULSAR 

... is a fast-paced, high-intensity 2D retro arcade game where you control a dying star as it collapses.  Use WASD/Arrow keys/Joystick to control the direction of gravity and collect powerups and orbs to push the walls back!

This game was made sporadically over 2 weeks using free time, is also open-source and was built using the usagi-engine!