In the 70's none as such, other than custom coded environments running on small mainframe type machines in universities and research labs.
In the 80's still very little, although MIDI came to the fore and so many sequence based platforms were developed to provide control over external hardware synths. Some went further and included score based input and control at what must be conceded to be inflated prices for the functionality provided.
of note at this point are pro-24 and its predecessors pro-16 and pro-12 on the Commodore 64 and later the Atari ST512/ST1024/Mega2St/Mega4ST (those numbers refer to the number of kB of RAM or the number of MB). Also Composer and Performer for the Mac (original series macs and the later SE series - small RAM footprint (less than 1MB))