Codename: Gordon is a Half-Life inspired side-scrolling action game created by Nuclearvision Entertainment. The game itself is an alternate vision of Half-Life 2, in which Gordon is tracking down the missing 3rd dimension.
The game was released on May 17th, 2004. It remained on Steam until late 2007, when the developers' website shut down and became and an advertising site. The game can still be installed on Steam by clicking this link.