Mind mapping

UMLet is a tool for creating UML diagrams. A free and open source program

Semantik is a free and open source program for creating mind maps for KDE, which helps you create presentations, dissertations, essays, reports

Minder is a free and open source software for creating mind maps

draw.io – free and open source, cross-platform program for creating diagrams and schemes , official desktop client diagrams.net

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