It’s perfectly reasonable for a consumer cloud storage provider to design a system that emphasizes recoverability over security. Apple’s customers are far more likely to lose their password/iPhone than they are to be the subject of a National Security Letter or data breach (hopefully, anyway).
I wish that companies like Apple could just come right out and warn their users: ‘We have access to all your data, we do bulk-encrypt it, but it’s still available to us and to law enforcement whenever necessary’.
So what is the alternative?
Well, for a consumer-focused system, maybe there really isn’t one. Ultimately people back up their data because they’re afraid of losing their devices, which cuts against the idea of storing encryption keys inside of devices.
You could take the PGP approach and back up your decryption keys to some other location (your PC, for example, or a USB stick). But this hasn’t proven extremely popular with the general public, because it’s awkward — and sometimes insecure.
Alternatively, you could use a password to derive the encryption/decryption keys. This approach works fine if your users pick decent passwords (although they mostly won’t), and if they promise not to forget them. But of course, the convenience of Apple’s “iForgot” service indicates that Apple isn’t banking on users remembering their passwords. So that’s probably out too.
I've been using Podverse but I'm not sure if it meets your requirements. I just use it in the browser when I'm on Windows. The Android app doesn't seem like a web wrapper. Its source code is available under the AGPL. I've been paying $18 per year for the hosted service, but they provide instructions on self hosting.
I'm expecting that everything that the statistical models reveal or make convincing results about which benefit the owners of the models will be exploited. Anything that threatens power or the model owners will be largely ignored and dismissed.
It means unstable (expect the beta version to be different than the alpha version in possibly fundamental and significant ways), and possibly buggy (let them know what problems you run into). If you're okay with that, have at it!
Some key quotes from the article: