According to the White House Blog, Whitehouse.gov has released some custom Drupal code - four modules, including NodeEmbed, "which improves accessibility of rich media for people with disabilities." (iTnews)
You can read more about the technicalities of NodeEmbed on the Drupal page here. Essentially, NodeEmbed allows everything you see on your computer screen to be accessed by screen reader software, including images.
I am a big supporter of open source, and the majority of programs I use at home are open. As the White House blog says, allowing everyone access to your code allows people to improve and better it who would never have had access otherwise. By tapping into the wide group mind of open source enthusiasts, code can be improved, made more efficient, and even adapted for uses far beyond the initial purpose.
If you are interested in open source software, check out the Open Source Initiative, and osalt.com, which can help you find open source alternatives to software you use every day.
For more on accessibility at Whitehouse.gov, check out their accessibility page here.