It's still up in code form on the old new forums, though:
http://www.puckdroppersplace.us/phpBB2/viewtopic.php?t=211
Sounds like a good way to transfer files to and from modern computers. I was initially wondering if the cassette adapter could record too, but I don't think any of them ever could. I wonder if one of the Atari guys figured out how to program a modernish system to output to cassette adapter directly, so you could type on the PC then have it write it. I seem to remember seeing something years ago for the TI994/a or C64.