Heimer
Heimer – free and open source, multiplatform and simple software for creating mind map, diagram, and note-taking tool
VYM (View Your Mind)
VYM (View Your Mind) – free and open source, multi-platform tool to generate and manipulate maps which show your thoughts
Freeplane
Freeplane – free and open source, multi-platform software for creating mind map, as well as knowledge management
XMind
XMind – free and cross-platform software for creating mind maps
FreeMind
FreeMind – free and open source software for creating mind map
Kate
Kate – free and open source, multiplatform and advanced text editor for KDE
FocusWriter
FocusWriter – free and open source, multi-platform and simple word processor that allows you to write without distraction
Gedit
Gedit – free and open source, simple and convenient, but powerful text editor for creating notes and programming from the GNOME project
ReText
ReText – free and open source, simple but powerful editor for Markdown and reStructuredText
Zim
Zim – free and open source, multi-platform graphical text editor for creating wiki pages