DotNetNukeDocs.com is no longer up and running as an editable Wiki. We encourage you to check out and contribute to the Wiki now hosted on DotNetNuke.com. http://wiki.dotnetnuke.com/
DotNetNuke Community Edition is free, and the most widely adopted and used version of the platform. It provides fully functional websites from personal all the way up through enterprise level applications.
DotNetNuke Professional Edition has a licensing cost of around $2,000 (US) per year and includes a number of benefits.