Under Windows

wincrt: This implements a console in a standard GUI window, contrary to the crt unit which is for the Windows console only.
Windows: This unit provides access to all Win32 API calls. Effort has been taken to make sure that it is compatible to the Delphi version of this unit, so code for Delphi is easily ported to Free Pascal.
opengl: Provides access to the low-level opengl functions in Windows.
winmouse: Provides access to the mouse in Windows.
ole2: Provides access to the OLE capabilities of Windows.
winsock: Provides access to the Windows sockets API Winsock.
Jedi windows header translations: The units containing the Jedi translations of the Windows API headers is also distributed with Free Pascal. The names of these units start with jw, followed by the name of the particular API.