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!
asciiflow - Infinite ASCII diagrams, save to Google Drive, resize, freeform draw, and export straight to text/html.
Minzel - Minzel is a beautiful and free mindmapping tool built for creatives and gives you the power to...
Core2D - A multi-platform data driven 2D diagram editor.
textografo - Online diagramming application which generate diagrams based on text and allows real time...
PathVisio - Open-source and free pathway analysis and pathway drawing software. Allows drawing, editing and analysis of biological pathways.