Have you ever tried to quantify what it is that you know about some specialized topic? How about what you and other people as a group collectively know about that topic? It's not always easy.
When I'm writing documentation for complex systems, I want to be sure I get everything in my head out into the reference document. To help make sure I've considered all of the important components and all of the things that need to be said about those components, I like to brain dump using tools designed for "concept mapping".
As shown here, a concept map is represented as a bunch of noun phrases like "the brain" or "knowledge", drawn as ellipses or bubbles. The noun bubbles then have links drawn between them, labeled with phrases that express the nature of the relationship.
This doesn't appeal to everyone, but I find it helpful for grouping and sorting things out, especially for complex systems. When I'm done with a mapping, I find that putting that knowledge into regular prose form just flows quite naturally. Even better, it tends to result in cramming the most useful information into the fewest words. That's powerful stuff.
If all I have to work with is web access, I'll turn to a cloud application at http://bubbl.us/. It has the basic features needed, and I like the way they've done keyboard shortcuts to speed work flow. However, it has some behaviors I don't quite like just because it's too different from my favorite mapping tool.
If I can, I'll use a PC that has my faithful old CmapTools on it. CmapTools is a program available from the impressively titled Institute for Human and Machine Cognition (yes, this is exactly where SkyNet really will be born). You need to register to download CmapTools but it's free. If the idea of dumping your brain content sounds useful and/or fun (it's both), you can learn more at http://cmap.ihmc.us/.