draw.io is online diagram software / flowchart maker, built around Google Drive (TM), that is designed to replace Visio(TM) in your online office setup.
draw.io provides you with a free tool to draw flowcharts, org charts, wireframes, UML, mind maps and more, then save them to your Google Drive. It uses the Google Drive Real Time collaboration functionality, so multiple users can work on the same diagram simultaneously.
draw.io is permanently free for all personal Google accounts.
Free alternative to Microsoft Visio
Sometimes you need to draw complex diagrams, in which Microsoft Office Organization Chart inside Microsoft Word cannot fulfill your need. And you do not want to pay the premium to get a copy of Microsoft Visio. Then draw.io is the perfect alternative. Not only because it is free, but also because it is cross-platform (Google Drive App).
Tips for using the product
draw.io does not have native application on either Android or iOS. In case you need to display the diagram on mobile devices, you will first have to export it to other file format, such as PDF, on a desktop computer.