It's yet another reincarnation of Pong. You control a paddle and try to keep the ball from getting past you. You score when the ball gets past your opponent.
When the program starts, the computer will be playing against itself. One or two people may take over at any time.
There are a few easter eggs hidden in the program. You can try to find them if you want. Looking through the source might help you find them.
Source: source.zip
x86 (Win32 Binary): pong.zip
Allegro DLL: alleg40.zip