The Texas Instruments 99/4a was too primitive to load programs, aside from cartridges, but because it booted to a command-line BASIC editor it had the ability to store its BASIC programs on a cassette recorder. We got one from Radio Shack ("Data Recorder," which was an ordinary tape deck) along with a special cable that let the TI take advantage of the microphone-pause that was built into the tape deck. You'd press record and note the counter position, and the deck would remain paused until you sent the command to start storing. Loading programs wasn't very reliable, but probably at least 80%.
Matt McIrvin had an atari cassette drive, too:
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