SequenceDiagram.org - Clean and fast online sequence diagram tool using scripting and Drag and Drop
TiddlyMap - An interactive concept- and mind-mapping plugin for the personal note-taking software TiddlyWiki based on the Vis.js library. It's free and open-source!
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
Wisdomap - Wisdomap Medicine is a study aid that helps medical students create differential diagnoses and suitable management plans from a presenting complaint and structured revision notes.
WebSequenceDiagrams - WebSequenceDiagrams is a web-based application that allows the user to use a proprietary language to define sequence diagram.
IOctopus - IOctopus is an online mind map service for a dive deep into the mind for the best ideas.