Corona supports Lua's module functionality for creating and loading external libraries. Currently, there are a number of libraries shipped with the SDK: ui.lua, movieclip.lua, tableview.lua, slideview.lua, scrollview.lua, etc. You can also create your own libraries and call them from your application.
Note: Corona only supports Lua-based modules at this time.
For more information see the Modules and Packages guide.
Also, see the External Modules Tutorial on the blog for a walk-through.
Is there no complete list of all libraries shipped with the SDK, ideally with with explications? I couldn't find something.