draw.io is a free online diagram drawing application for workflow, BPM, org charts, UML, ER, network diagrams. No login or registration are required and features include the ability to save locally (including svg), a range of stencils, .vsdx, Lucidchart and Gliffy import and real time diagram sharing.
- It is very convenient and contains many features.
- It's really easy to use, and has so many features for a web app.
- It's free and includes many of the same features.