Phagefight

In Phagefight, you are in control of an army of bacteriophage. Small viral organisms engaged in an epic battle over an area a few microns wide.

It is a small turn-based strategy game similar to Ataxx. The board is 7x7 squares, and there are 20 different boards differing in obstacles and initial starting places. In turns, players (or player vs. computer) move one of their pieces. If the piece is moved to an adjacent square, the piece is duplicated, otherwise the piece moves up to 2 squares away. All enemy pieces adjacent to the landing square are converted to the player's colour. If the board becomes full or a player doesn't have any legal moves, the player with more pieces wins; it's also possible to win by eating all of the enemy's pieces.

Besides the 20 different boards, the background colour and cycling speed can be customized, and the AI difficulty and aggressiveness can be tuned. Although the game is designed for then-modern PC's, it could be run in an old XT model and it could fit in a 5.25" DD 360 KiB disk.