asciiflow - Infinite ASCII diagrams, save to Google Drive, resize, freeform draw, and export straight to text/html.
Playscii - Full-featured ASCII art and graphic editor and game creation tool
Lekh Diagram - Lekh Diagram empowers you to express your idea on iPad and iPhone simply by sketching shapes with...
draw.io - Online diagramming application
Core2D - A multi-platform data driven 2D diagram editor.
UMLGraph - UMLGraph is a professional automated drawing tool that allows the designers the declarative specification and drawing of UML class and sequence diagram.