Betamax

Betamax is a side-scrolling shoot-'em-up that sees the player at the helm of a fighter ship in hostile space, fighting for survival against wave after wave of attacking aliens. The premise? - take them down, pick up the energy balls they leave behind, and exchange them for ship upgrades.

These upgrades are handled by a power-up system similar to Gradius: collecting an energy ball advances the upgrade meter, and the player may choose to activate the currently highlighted upgrade at any time. Each game begins with three lives; active ship upgrades stay in effect when a life is lost, although they do wear off after a while. On the other hand, some of them have additional levels which improve the power-up's effect if applied more than once.