Gnat for Linux, MS-DOS, Windows9X, and Windows NT
Gnat for Windows with AdaGIDE as integrated development environment
Gnat for Linux/Debian
Other platforms
Ada Tutorial at Georgia Tech
Ada Lovelace Tutorial by David Wheeler (local and outdated version at Stuttgart)Ada Lovelace Tutorial by David Wheeler (latest version at AdaHome)
Ada Lovelace Tutorial by David Wheeler (latest version for download at AdaHome)