Dr. T's Music Software is one of the most famous companies which was specialized in all kind of musical software for computers. The company is now out of business, but the former president Emile Tobenfeld (aka Dr. T.) is still maintaining a tribute site for the company.
On the Amiga they coded for instance Boombox which was a very early (and successful) attempt to write a music tool for beginners. It has a very easy to use GUI and every newbie can get along with it. Of course there was so much software for the experts: Midi Recording Studio was a prefessional MIDI program, Keyboard Controlled Sequencer was a sequencer for professional musicians.
Dr. T. brought us many masterpieces which will never be forgotten by music software enthusiasts. | 
Boombox 1.0
Midi Recording Studio |