Space Adventure (1988)

A top down exploration shoot-em-up game where the player has to collect 4 crystals from a hostile alien craft to their scout ship in order to destroy the alien vessel. Keys are required to get to the crystals, and there are a lot of enemy androids roaming the alien ship, each of which must be destroyed before the next room becomes accessible. The original version of the game was by Andrew and Roger Thomas for the BBC Micro and it was ported to DOS by Robert Schmidt of FireBall Software Ltd.