Sibelius is a home computer program designed as a scorewriter. Named for the Finnish composer Jean Sibelius, it was first launched on the Acorn computer system in 1993, created by a specialist company which was founded by British twins Ben and Jonathan Finn.
(Contrary to popular belief, the name 'Sibelius' was not a pun on the inventors' surname of 'Finn' (which is, in any case, an Irish name). 'Sibelius' was chosen for its futuristic sound, and the inventors apparently didn't spot the Finnish connection until later.)
Since then, it has grown to become the world's most widely-used scorewriting package, currently in version 3 (for PC and Macintosh).
The launch of Sibelius significantly heated up the 'home and professional scorewriter' market, previously dominated by Finale.
