Razerwire: Nanowars

Survive the endless waves of invading aliens, and when you lose, use the resources you've gained to upgrade RazerWire and keep fighting!
RazerWire: Nanowars is a unique bullet-hell style game where you don't so much shoot enemies as use a wire connected to a generator as a weapon, cutting through enemies with a sharp monomolecular filament.

With each wave, the difficulty level increases! Opponents with new weapons and better armour appear, and this is where upgrades come to the rescue. With the points you earn, you can upgrade your weapon and also buy useful powerups.