Codename: Gordon is a third-party, flash animation side-scrolling game made by Paul Kamma (X-Tender) and Soenke Seidel (Warbeast) for Nuclear Vision and Valve Software. It is distributed over Valve Software's Steam delivery system. Although it was not created by Valve, on Steam it is listed on the official Valve products page, along with the Half-Life series, Counter-Strike, and Team Fortress Classic. The game was made available before the official release of Half-Life 2 as a form of publicity, and is available free of charge to anyone with a valid Steam account.

Codename: Gordon is an "alternative take" on the storyline of Half-Life 2. The player controls Gordon Freeman in and around City 17, battling Combine forces, headcrabs, and other familiar enemies while encountering allies such as Alyx and Eli Vance. However, Codename: Gordon is quite unlike Half-Life 2 in that Codename is exclusively two-dimensional ("an entire dimension is missing!").

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