Sewer

Shoot incoming monsters with your serial mouse in the shareware title by Michael J. Wilson released in 1994. Per the author it is a completely sadistic and totally xenophobic blast-the-alien-blobs game. There were 2 versions, a scaled down PD version with a code to become the full shareware version. If you wanted the full sounds, end0game sequences and intros and source code you chose the shareware key.

The first manned mission to Mars made an amazing discovery. We are no longer alone in the universe. Unfortunately we share it with a bunch of primeval simple, single celled protozoa less than a millimeter across, which is the most advanced form of life found in the warm craters of Olympus Mons, a very large and active volcano. They are invading the main server system and if allowed to grow there for 24 hours, they will multiply and take over the entire planet. You pulled the short straw and have to take them out.