Modelio : Modelio is an open source modeling environment (UML2, BPMN2, ...). Based on a 20-year track record of high end commercial products, Modelio delivers a...
Pingendo : The simplest app for Bootstrap prototyping. Create quality HTML prototypes quickly, using popular open source tools like Bootstrap, LESS, Fontawesome ...
Origami Studio : Origami is a free tool for designing modern user interfaces.
Arora : Arora is a lightweight cross-platform web browser. It's free (as in free speech and free beer). Arora runs on Linux, embedded Linux, FreeBSD, Mac OS X...