The latest Humble Bundle seems to be doing well and has, as has now become customary, added on another game "Dungeons of Dredmor". The bigger news however, is that the latest Humble Bundle has also added on the source code of its major games, Darwinia / Multiwinia, Uplink, and DEFCON.
This isn't like previous source code releases though; the ones that happened with the first bundle, of which a number of games were released under the GPL. The games aren't being "open sourced" in the traditional sense. Generally, open source has come to mean licenses such as the GPL / LGPL, MIT, Apache or MPL, however open source simply means that the code for the software is available. The license controls who can use the source code, how, for what and under which conditions.
Introversion has been selling the source code of their games for quite a while now, however their license does not permit redistribution of the source code, nor modification and distribution. One can distribute the modifications to the code if large enough; however any game created using Darwinia as a base will need to check if Darwinia is installed before running.
Being a Humble Introversion Bundle purchaser gives you access to the source code, and the opportunity to access the source code repository directly, and the ability to make your own branch. You also get access to the developer forums and Wiki.
The source code is a brilliant tool for those who are trying to get into creating games themselves, as you can see the code of a successful commercial game.
You can buy the Humble Introversion Bundle from the Humble Bundle website. Remember that the usual awesome Humble Bundle benefits apply, all games available at any price you want, the games are DRM free, the games are available for all platforms, Windows, Linux and Mac OSX, and each purchase includes a customizable donation to charity.