I find myself in a lot of situations where information isn't coming to me in a particularly organised fashion - interviews, presentations with several presenters, being on the receiving end of braindumps, etc. For those situations, I really need a mindmap app to be able to reorganise information with minimal effort into a structure that makes sense to me. It's a not-cheap, Apple-only app, but it can output into a variety of formats if I want to consume it on some other platform.

It also works well as a presentation tool if I don't know the audience's knowledge level. Rather than be tied into e.g a sequence of slides, using a mindmap tool I can skip over stuff the audience already knows, while still having the content there (just not visible) if I need to drill down deeply. I can go from receiving an unstructured braindump to presenting that same info in an organised fashion within a few minutes

I used to use Freemind and Freeplane, but the lack of an iOS option was a killer.

For most other situations, I find Evernote is great