100+ comments, and nobody mentioned type-ins:
Common in magazines, you'd have pages with listings that users could type in, save, and then run (in that order!).
Well... usually including some corrections. The usual typo's, but even listings as published contained errors sometimes.
BASIC was very suited for this as many keywords are plain English or -like.
It's only later this got replaced by cover tapes etc.
And in the NL, there was a thing called BASICODE:
https://en.wikipedia.org/wiki/BASICODE
Which was an attempt to make a standard dialect that different computers could interpret, and/or convert into their own machine's BASIC.
A late-night radio program (NOS Hobbyscoop) would often end its transmission with some minutes of tape-loading sounds. Users would record this on tape, run it through some conversion program, and RUN. So the same program as transmitted over the air, could then be run by C64, ZX Spectrum, MSX, Amstrad CPC users etc.
Iirc it wasn't that popular compared to other ways of obtaining software. But computer users @ the time were eager to do & try anything they could get their hands on. Today's internet info-overload didn't exist then.
And of course radio had a wide audience. Interesting programs could thus be distributed among many users quickly.