What is it?
Visio is a full-featured diagramming tool that is part of the Microsoft Office family of applications. It fills the gap between PowerPoint and full-blown CAD packages, allowing straightforward creation of organisation, flowchart, room layout diagrams, and technical drawings like network and electrical schematics.
Visio doesn't replace PowerPoint - PowerPoint is straightforward to use for presentation graphics where simplicity is important. Visio is better at more complicated diagrams which need to be altered frequently, like organisation charts.
As a rule of thumb, if PowerPoint produces what you need, carry on using it. If you're frustrated with PowerPoint's abilities, you should try Visio.
What does it work on?
How to get it
If you use the Managed Windows 7 Desktop, Visio is pre-installed and available via Start>All Programs. Do not download from this page if you use the Managed Desktop. If you use an unmanaged machine: