Nibbles.bas under Virtual PC
Just like Gorilla.bas, Nibbles.bas is a source code based QBasic game that shipped with MS-DOS 5, Windows 95 and others. Nibbles is a version of the classic 'snake' game where you control a snake that must avoid running into walls and itself, which is made harder by the fact that the snake grows in length every time it eats something (in this case numbers).
Nibbles runs perfectly under Virtual PC:
Nibbles has 20 levels, and after the 20th level you just play the 20th level over and over and over (yes - I have played this game far too much). Nibbles features some particularly nefarious levels (in the higher levels there are walls that are 'perforated' and require a perfect aim to pass through). It also supports a two player mode where two snakes are on the screen at the same time.