Tableau Desktop
full desktop environment for creating workbooks. Can create (normal) and packaged workbooks. Can upload to any server-side software
Tableau Server
used to Publish Dashboards
Tableau Reader
(free) - to open Tableau Packaged workbooks locally
Tableau Public
(free) - to create workbooks that you can ONLY upload to Tableau Public (see below), can ONLY connect to XLS or Text files. Can ONLY upload to Tableau Public