Codename: Gordon

Codename: Gordon, also known as Half-Life 2D, is a two-dimensional Flash sidescroller shooter game made by Paul "X-Tender" Kamma and Sönke "Warbeast" Seidel. The game was produced on behalf of Nuclear Vision, and was distributed free of charge over Valve Software's Steam online delivery system as a promotional title for the then-upcoming Half-Life 2. The game has since been removed from Steam's storefront due to factors related to the developer's bankruptcy.
The game started off as a fan project of Paul Kamma and Sönke Seidel, the concept being inspired by various Half-Life 2 advertisements. Soon after, the two started working on Codename: Gordon on behalf of Nuclear Vision. The company also presented the game to Valve, the developer team of the original Half-Life series, who later distributed the game through Steam.