Xmind - Xmind is a brainstorming and mind mapping application.
Foxit Reader - Foxit Reader is a free and light-weight multi-platform PDF document viewer.
MindMeister - Create, share and collaboratively work on mind maps with MindMeister, the leading online mind mapping software. Includes apps for iPhone, iPad and Android.
DjVuLibre - DjVuLibre: Open Source DjVu library and viewer
Coggle - Coggle is a simple, beautiful, powerful way of structuring information.
DjView4 - Standalone viewer for DjVu files.