Bit Tanks is a 2-D arcade style defense game similar to games like Missile Defense. It's designed to be enjoyed in short bursts of 3-5 minutes, which makes it a great option when you don't have time to dig into a deep narrative. Although extremely simple to pick up and play, it has the nuance and subtle mechanics to keep a hardcore player entertained as well.
You can pick up Bit Tanks at www.joshuahriley.com for whatever price you think is fair. Bit Tanks is provided DRM free and can be downloaded as many times as you's like.