Mind mapping

Heimer – free and open source, multiplatform and simple software for creating mind map, diagram, and note-taking tool

VYM (View Your Mind) – free and open source, multi-platform tool to generate and manipulate maps which show your thoughts

Freeplane – free and open source, multi-platform software for creating mind map, as well as knowledge management

XMind – free and cross-platform software for creating mind maps

FreeMind – free and open source software for creating mind map