Remember QPong for Quake2? This is a start at recreating it. It's simple: A long map, 2 goals and an eight foot ball. Shoot the ball into the enemy's goal. Some weapons work better than others. Be careful though, getting too close to the ball can seriously damage your health! Currently the game registers goals and keeps score, and is one of the few HL2 mods to have a Linux server.
You need this file to play PongSource. It is zipped with 7zip. There is a readme.txt. Read it for install instructions and changelog.
Missing textur much?
When PongSource was new and had only one ball, there was no texture on it.
But when PongSource evolved, the checkerboard texture became cult.