Gaming classic Wolfenstein is 20 years old, and to celebrate, John Carmack has done a director's commentary for the game, which is now playable online.
I've just had the pleasure of watching 25 minutes of game-programming kingpin John Carmack reminisce and talk about the development process for the seminal Wolfenstein 3D. A thoroughly enjoyable video from a technical standpoint, although I do wonder if John Carmack is a real-life version of The Simpsons' Professor Frink.
An online version of Wolfenstein is now available, too (warning: press x to shoot, not Ctrl).
If you want to dig in to the online version's source code, viewing this page is a good place to start.
Best of luck maintaining productivity for the rest of the week.