yEd is a free general-purpose diagramming program with a multi-document interface. Developed by yWorks
License: Free
Apps available for Mac OS X Windows Linux Online BSD
VisiTouch helps you view and convert to PDF your MS Visio diagrams for iPhone. Developed by Darsoft Inc.
License: Commercial
Apps available for iPhone iPad Discontinued
yEd Graph Editor is a versatile tool suitable for creating a wide variety of diagrams on multiple platforms, while VisiTouch is designed for touch interfaces with an emphasis on collaboration and media integration.