Final Fortess
Final Fortress is a You da Games production. It’s a Fast thrilling action shooter. You start with a canon to defend your city but you can upgrade your power building new units. Each level allows you to receive money for these upgrades and the needed reparations. With Final Fortress you won’t be able to stop shooting.
Controls: use the mouse to aim and the left buttom to shoot (you can hold down the left buttom to prolong you mouse life), you can also use some shortcuts with your keyboard: space to repair or sell individual units, R to repair all units, B to build units.
Play the demo version with two phases each with 5 levels.
I have just completed these 10 levels 
