(pronounced VIZ-ee-oh)
Formerly Visio before its acquisition by Microsoft, this product has by any name generally been the standard program for drawing diagrams of every sort: circuitry, networking, org charts, and more.
Microsot Visio is sold in various versions which include different templates, different stencils, and wizards for doing different tasks: Technical, Professional, Standard, etc. The major difference between Microsoft Visio and earlier versions of Visio is that Microsoft has added features to integrate it more closely with other MS products.