Bio Menace was one of my favourite pc games back in the old 486 days.

Apogee Software, Ltd. has released Bio Menace as freeware. Originally released in 1993 Bio Menace is a side scrolling action game in which you take on the role of CIA agent, Snake Logan. Mutants have overrun Metro City and it's your job to destroy and find the source of these mutants.
The game features old EGA graphics that look good for when the game was developed, it also utilizes an early game engine designed by Id Software. There are plenty of levels, powerups and mutants to keep you busy in this action filled game.
Its now abandonware (I think that is the term for discontinued software.)

Free Download