Lucidchart is a diagram creation web app that has a lot of great features and uses. It is built on HTML5 and works on any browser and device. It is completely web based, uses drag and drop functionality, has group chat and comments on projects, has revision history, ability to embed it in other apps, and integrates with Google Drive. It also supports Microsoft Visio import and export.
It can be used for mind mapping, process charts, network diagrams, graphic organizers, floor plans, programming flow charts and much more. This is useful for schools, IT departments and administration.
There are hundreds of shapes, drag and drop, export (PDF, PNG, JPG), real time collaboration, and much more.
There is also a free Education Account that has all of the features of the premium accounts.
It also has templates and examples: Flowcharts, Venn Diagrams, Graphic Organizers, Mind Maps, Org Charts, Wireframes / Mockups.