Diagramo is pure HTML5 (canvas) flowchart software. It is open source, so anyone can take it and use it under GPL 2.0 version.
You can find Diagramo sources on either Bitbucket or mirrored on GitHub.
Firefox: http://superuser.com/questions/23134/how-to-turn-off-the-firefox-cache
Chrome: http://stackoverflow.com/questions/5690269/disabling-chrome-cache-for-website-development/8290697#8290697