[PC, Steam] Free - Polygoneer (93% Positive on Steam) @ Steam

If you add it to your account before 20 June 3:00 am US time, it is yours to keep forever.
Very minimalistic game but highly rated.

From the website:

• POLYGONEER is an arcade reflex based game. You should defend yourself from polygonal enemies that come from all sides, hitting them with the right color shot, one miss and its the end.
• Perfect to play when you want to test or improve your reflexes, or while you are on a queue for another game, this is a small and replayable game. The objectives are to beat the 5 stages, get on top of the leaderboards, unlock achievements and beat personal scores and times.
• Test your reflex destroying the enemies using the right color shot in one of the 5 levels (or in the hidden HELL level).
• Survive and score by shooting the right enemy with the right color shot.
• Get bigger scores by not missing any shot, the multiplier increase for every 10 enemies destroyed. If you miss the color or the shot the multiplier return to zero.
• Unlock the next stage by surviving 30 seconds on the previous one.
• Fast paced arcade gameplay.
• 5 different stages and a hidden hell stage.
• Leaderboards for each stage.
• Polygonal graphics.
• Great to play both with joystick or keyboard.
• 6 Amazing electro-hardcore original tracks.
• Steam Leaderboards, achievements, cloud save and trading cards (when aproved by Valve).
• 2 different languages (English, Português)

Enjoy!