Ricochet

Ricochet is the undeserved black sheep of Valve's games and their first foray in quirky FPS games that eventually led to Portal and Portal 2. Apparently, it was an experiment in which they spent just three months making a game, with the intention of supporting it long-term to see what would come out the other side. Somehow they never got around to the whole "updating" thing, and the game stands today as the origin of Team Fortress 2's crazy updating system, as well as a means of making Robin Walker flinch upon mentioning it.

Unused Female Player Model
An unused female player model exists in the game's files. The model appears to be complete, minus having her own “head decapitated” model.

Unused Powerups
There are models for two unused powers, “curve” and “visual”. When opened up in a model viewer, the powerups are the TFC soccer/football ball and the TFC present model, respectively.

Disc View Model
The disk thrown by the player has a “view model” in the game's files that is never seen in-game, but when looked at in a model viewer, it is the Half-Life grenade's view model.