I played games on a Commodore 64 from cassette tapes, in principal you could record games onto a blank cassette but it was very flaky. Good times though.
I did this all the time... even used a double cassette deck to make copies... azimuth was the problem if the heads were aligned different.. so you used a small screwdriver and the top of the cassette had a small opening, this is where you had to align the heads by listening till it didn't sound distorted.. fun times
Then came a nifty upgrade called "LED control" which installed a red LED next to that screw so all you had to do was turn until it was brightest, significantly reducing ?LOAD ERROR. Good times.