MindTouch Deki Wiki is the most popular vendor backed wiki. It is free open source software (FOSS) and is commonly used for online communities, collaboration, or for building collaborative web applications. It’s built completely on open standards (XHTML, JSON or PHP). It was the first OSI-approved commercially supported open source wiki (released under GPL 2), and is now the only open wiki platform. It has the most complete API that features 99 REST based methods and a web-service extension model that makes it possible to create mashups with many other applications, widgets, and/or data stores like Google Maps, Digg, Flickr, YouTube, MySQL, widgets from WidgetBox, etc.

I would like to nominate the social networking site http://www.vois.com and since I am their best employee it is a good thing I didn’t pick a different site!