Draw. IO is a powerful and concise online drawing site that supports diagrams, UML diagrams, architecture diagrams, prototypes, and more. Support Github, Google Drive, One Drive and other network disk synchronization, and permanent free. If you find the Web version inconvenient, draw. IO also offers a multi-platform offline desktop version for download.

The web version

app.diagrams.net/ 

The desktop version

Github.com/jgraph/draw…

Github.com/jgraph/draw…

Similar product processon

www.processon.com/