Defend against a descending formation of alien invaders.

• Arrow keys or A/D (or the on-screen buttons on touch) to move left and right.
• Space, or the fire button, to shoot upward.
• The formation marches side to side and drops lower each time it hits an edge - shoot every invader before it reaches you.
• Dodge the invaders' return fire. You have a limited number of lives, shown in the HUD - lose them all and it's game over.
• Clear a wave to advance to the next, tougher one.