Gopher Blue was the main one I used back then, even remember having to run a program to convert the 7bit ascii stream back to 8bit binary after receiving it from there! They had a large repository of AtariST utility programs! All part of running a Citadel BBS for the AtariST community in my area! I got access through our local university's dial-up system. Going from 300baud to 1200baud was a real treat back then!