Modelio - Modelio is an open source modeling tool supporting natively UML, BPMN and model exchange with XMI.
asciiflow - Infinite ASCII diagrams, save to Google Drive, resize, freeform draw, and export straight to text/html.
Diagramo - Diagramo is an online flowchart software - diagrams (create, edit and share)
Core2D - A multi-platform data driven 2D diagram editor.
ARIS Express - ARIS Express is based on the proven ARIS methodology and industry standards.
PathVisio - Open-source and free pathway analysis and pathway drawing software. Allows drawing, editing and analysis of biological pathways.