iD Software is really forward thinking tech company in that it releases the source code for its older game engines and level tools. Don't take my word for it, check out the code they have released on github.

This kind of thing should be applauded because when game companies release the source to their games it means that the odds you will be able to play the games you love in the future is pretty good. Plus its awesome to play a game you love on any platform you want. Its also a great way to learn how a top notch game engine operates.

Intro Fabien Sandlard a guy with an awesome hobby, he looks at released game source and blogs about it. Fabien has reviewed Duke Nukem 3D, Quake 3, The Original Doom 3, Doom & the Wolfenstein iPhone port code and more.

Recently he looked at the source for Doom 3: BFG Edition. Doom 3: BFG Edition is interesting because iD back-ported code from Rage into Doom 3: BFG Edition. They also had to get Doom and Doom 2 running inside the Doom 3 code itself, which is an interesting technical feat. The article is pretty interesting and seems accessible to non-programmers(full disclosure, I am in fact a programmer).

A cool bit I found Fabien's article:

"Overall the reader gets an immediate understanding of each part of an algorithm and I hope it will inspire people to write better code: Modern software development is not about being an ace programmers anymore. It is about being a team player that empowers co-workers with: Elegant design. Easy to read and commented code implementing it. Doom 3 BFG ranks high on both those metrics. "

Fabien is spot on here. Wizardy in code is all well and good, but writing good code anyone can understand and maintain is much better when you work on a team.