asciiflow - Infinite ASCII diagrams, save to Google Drive, resize, freeform draw, and export straight to text/html.
Modelio - Modelio is an open source modeling tool supporting natively UML, BPMN and model exchange with XMI.
Core2D - A multi-platform data driven 2D diagram editor.
Diagramo - Diagramo is an online flowchart software - diagrams (create, edit and share)
PathVisio - Open-source and free pathway analysis and pathway drawing software. Allows drawing, editing and analysis of biological pathways.
UML Designer - UML Designer provides a set of common diagrams to work with UML 2.5 models.