Basic:

Includes all core components: Tabs, Modules, Users, Roles, Forums, Skins, and Administration for all of these, as well as other features.

 

Professional:

Includes all "Basic" features, as well as: Calendar, Content, Newsletter signup, Email sending, Member list, RssReader, Administrative Uploading files, Weather Forecast, Who is Online

 

Enterprise:

Includes all "Professional" features, as well as: Amazon products gallery and search, Multi-Language support, Polls, Sql Web Query administration tool for advanced database scripting and reporting