Xmind - Xmind is a brainstorming and mind mapping application.
Beyond Compare - Beyond Compare allows you to compare files and folders.
MindMeister - Create, share and collaboratively work on mind maps with MindMeister, the leading online mind mapping software. Includes apps for iPhone, iPad and Android.
WinMerge - WinMerge is an open source differencing and merging tool for Windows.
MindManager - With MindManager, flexible mind maps promote freeform thinking and quick organization of ideas, so creativity and productivity can live in harmony.
Meld - What is Meld? Meld is a visual diff and merge tool targeted at developers.