This past Sunday marked the 20th anniversary of "Wolfenstein 3D," the game that essentially laid the groundwork for the first-person shooter genre and influenced many of id Software's titles for years. To celebrate the milestone, Bethesda (which acquired iD Software in 2009) has released a free, browser-based version of the iconic game where you'll have to shoot your way out of a Nazi stronghold during World War II.

Although Wolfenstein wasn't id's first 3D shooter --- Hovertank and Catacomb 3D came before it --- it was a major improvement as it moved from a 16-color EGA to a 256-color VGA graphics palette and used 2D sprites mapped from eight perspectives to produce a better illusion of 3D objects. It also established the fast-paced action commonly expected in the genre, encouraging exploration and rewarding players with various treasures, hidden rooms, and even some easter eggs like a Pac-Man level.

Doom came a year later with better graphics and network play, while 3D Realms and Valve followed with titles such as Duke Nukem 3D in 1996 and Half-Life in 1998. Together with the advances in 3D hardware technology these companies helped spawn a PC gaming industry now worth billions of dollars.

Along with the free, web-based game Bethesda also published a 25-minute developer commentary track where industry legend John Carmack talks about his memories of the game and the early days of id Software.