Before the Doom and Quake series really brought fast-action first-person shooters into the gaming mainstream, there was one game that set the tone for what was to come: Wolfenstein 3D. The progenitor of an entire gaming genre turns 20 years old this month, and to celebrate the anniversary, a free browser version has been unleashed onto an unsuspecting web. All three of the main "episodes" are present here, with each including 10 sub-levels. It's a faithful — as far as we can recall — reproduction of the original game, albeit with the added extra of allowing mouse-based control as well. We advise sticking to the default keyboard controls, the mouse can feel extremely unintuitive given the only camera control you have is lateral (there's no up or down motion).

Programmed by John Carmack and designed by John Romero, Wolfenstein 3D tracks the tale of a captured US spy, BJ Blazkowicz, as he makes his escape from Nazi imprisonment during World War II and proceeds to raise a little hell on his way out. If you haven't played it already, trying out the browser version is a must.