Protracker was a music program for the Amstrad CPC written by Crown, which was based on digital instruments (samples) instead of PSG (chip) sound.
Out of wave tables it mixed three channels into one 4 or 8 bit channel, which has been output via the CPCs' internal PSG or the Digiblaster (printer port) DAC-extension.
Protracker was a competitor of Digitracker and had a better playback quality, as it used a different technology for rendering the samples.
The disadvantage of this technology was, that there were only about 50KB free for samples instead of about 62KB (Digitracker).
Background Story
The official reason why Protracker has been developed, was, that Crown had a fight with Prodatron at this time (Prodatron left BENG! etc.).
As Prodatron had already developed Digitracker for SymbiosiS and wanted to distribute this program via Kangaroos company New Age Software, Crown decided to write a competitive product for free, so that Kangaroo and Prodatron won't be able to earn any money.
He released Protracker and was successfull: Prodatron decided to change the status of Digitracker from commercial to shareware.