A GUI is an acronym for graphical user interface. GUIs use windows (forms) to make programs. The Lazarus IDE works with Windows, Mac OS X, Linux and FreeBSD. Other OS maybe supported in the future. This makes porting applications, from one OS to another, very easy. The IDE and coding for GUI Apps are very similar to Delphi. All code is available for download at http://www.schoolfreeware.com Free Pascal and Lazarus can be downloaded at freepascal.org