This month is the 20th Anniversary of Wolfenstein 3D. To celebrate id Software and Bethesda have given us all a free browser-based version of its seminal shooter. John Carmack has also given a director's commentary, full of the usual fascinating Carmackchat. You can play the snazzy HTML 5 version of Wolf 3D if you're browsing in Firefox 10, Chrome 16, Internet Explorer 9, Safari 5, or newer. Fingers crossed that your work computer is updated vaguely frequently. id Software got distracted by Doom and Quake after the release of a Wolf 3D prequel, but the series returned in 2001 with Return to Castle Wolfenstein from Grey Matter and Nerve Software. Splash Damage followed this with the superb free multiplayer spin-off Wolfenstein: Enemy Territory, then the last entry in the series was Raven's Wolfenstein in 2009. The iOS version is also going temporarily free in the App Store some time later today. Here is the Link