Moqups - The most stunning HTML5 app for creating resolution-independent SVG mockups, wireframes & interactive prototypes for your next project
Diagramo - Diagramo is an online flowchart software - diagrams (create, edit and share)
LucidChart - LucidChart is the missing link in online productivity suites. LucidChart allows users to create, collaborate on, and publish attractive flowcharts and other diagrams from a web browser.
Modelio - Modelio is an open source modeling tool supporting natively UML, BPMN and model exchange with XMI.
Axure RP - The prototyping and specification software used by 87% of the Fortune 100. Beyond mockups, design interactive prototypes for business solutions, websites, and applications.
UML Designer - UML Designer provides a set of common diagrams to work with UML 2.5 models.