There are many different Sky operating systems. All are produced by Enigma Productions. * Sky (1991) * Sky 2.0 (1994) * Sky 3 (1996) * Sky 4 (1998) * Sky5 (1999) * Sky6 (2000) * Sky7 (2002) * Sky8 (2003) * Sky9 (2006) * Sky10 (2008)