Lucidchart is an online diagram and flowchart software that supports Microsoft Office Visio import and can work on any operating system. The easiest way to draw flowcharts, wireframes, UML diagrams, network diagrams, mind maps, site maps and more. Work together in real time with your team and clients! 

yEd Live is a free diagram editor web application that runs in the browser and lets you quickly create, import, edit, and automatically arrange diagrams.