Eyop!
I saw this feature request the other day and thought to myself that, indeed, it is strange that there is no open source version of audio.com around. So I made one:
To be clear, this isn’t a complete clone, or anything remotely close to it; the entire social aspect of audio.com is missing. But if you want to have a server that you can upload audio to or backup your projects to, using the relevant buttons found in Audacity, this is an option. Setup instructions here, I’ve tested it in Audacity 3 and Soundscaper and it works, but it doesn’t work in Audacity 4 yet (relevant bug – though I suppose if you intercept the audio.com DNS, it might work).
May this be useful for someone.