I was born late enough to avoid that era. Probably the most primitive thing was writing on paper a 6502 assembly program, converting it to machine code HEX values, and using a HEX keypad to program into battery backed RAM module...which you would then drop into the runtime HW. I controlled a bunch of I/O LED’s - made the “Knight Rider” effect. At 14 I thought it was pretty cool.
Interestingly, as I grew up in the UK - every phone call cost money, so we didn’t really get into the whole BBS/modem thing.
I remember entering code via switches in 1965.