PlantUML is an open-source tool allowing users to create UML diagrams from a plain text language. Developed by Arnaud Roques
License: Open Source
Apps available for Mac OS X Windows Linux Online Android
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
VisiTouch is geared towards users looking for an intuitive, visually-oriented diagramming tool, while PlantUML offers a text-based approach that is better suited for developers and technical users who need version control and extensibility.