Xenon - Originally released in 1988 by The Bitmap Brothers was a single player vertical scroller on Atari ST.
Xenon 2 Megablast also a vertically scrolling shoot 'em up. Unusual for the genre at the time, the player's spaceship can reverse the scrolling of the play area for a limited distance; which is used in the game for defeating bosses, avoiding enemies and escaping dead ends. This game consists of five levels which are each divided into two sections.
The game has a generic sci-fi theme and almost no plot, focusing instead on presentation and gameplay. Indeed, it was the quality of the music and graphics that led to the game's memorability.