Since we already have excellent tools that follow the UNIX philosophy then I would opt for being a LEGO assembly guy by combining these:
- Management of backups themselves: borg / restic (or rustic) / duplicati / duplicacy etc. Last I evaluated them borg offered the most in one package. I like restic a bit more but it's a fair bit slower than borg, sadly. `rustic` aims to fix that but it's a volunteer effort and the author has bursts of productivity that are not on a stable schedule. I use rustic as a backup of my main backup tool (borg) but for now dare not use it exclusively.
- Management of keys / secrets / passwords: my semi-vulnerable setup is to just upload my borg repo key to my Linux server and also have it pinned in one of my private Telegram channels. That one could be done better but I haven't done research. Probably something close to gpg (many modern alternatives with less friction but I forget names; I have them bookmarked though) to make sure even your keys are properly protected. One possibility is a password vault like keepass[x] or Enpass or others.
- Management of storage: I use a local Linux server (EDIT: I have a very non-redundant and basic ZFS setup) and 5+ cloud storage services on the free tier. All of them have at least 5GB and my borg repository is barely 150MB I think. That includes ~20 past backups.
The way these could be combined is mostly by having a top-notch GUI and CLI (so we serve different kinds of people) that allows for granting access to cloud storage servers, asks optionally for a local storage server (NFS, Samba, WebDAV etc.) and just does everything else by itself. It's very doable.
Regarding the first two points, maybe Kopia [0] come close. It has both GUI and a CLI. For the GUI, it saves your backup key for you (although I have to admit I didn't check how much securely stored it is), but you still have to keep a copy yourself in a password manager or similar in case you need to access your backup from some other machine. AFAIK, for the CLI you are completely on your own regarding secrets management. But it's also true that the average user doesn't have servers to backup, so the GUI would be fine.
Regarding the management of storage, what do you mean? Kopia already supports different "storage backends" out of the box which can be configured via the GUI. Do you mean that you would like it to be able to merge the storage of different storage providers, so that you can use multiple free tiers to get the storage space you need?
- Management of backups themselves: borg / restic (or rustic) / duplicati / duplicacy etc. Last I evaluated them borg offered the most in one package. I like restic a bit more but it's a fair bit slower than borg, sadly. `rustic` aims to fix that but it's a volunteer effort and the author has bursts of productivity that are not on a stable schedule. I use rustic as a backup of my main backup tool (borg) but for now dare not use it exclusively.
- Management of keys / secrets / passwords: my semi-vulnerable setup is to just upload my borg repo key to my Linux server and also have it pinned in one of my private Telegram channels. That one could be done better but I haven't done research. Probably something close to gpg (many modern alternatives with less friction but I forget names; I have them bookmarked though) to make sure even your keys are properly protected. One possibility is a password vault like keepass[x] or Enpass or others.
- Management of storage: I use a local Linux server (EDIT: I have a very non-redundant and basic ZFS setup) and 5+ cloud storage services on the free tier. All of them have at least 5GB and my borg repository is barely 150MB I think. That includes ~20 past backups.
The way these could be combined is mostly by having a top-notch GUI and CLI (so we serve different kinds of people) that allows for granting access to cloud storage servers, asks optionally for a local storage server (NFS, Samba, WebDAV etc.) and just does everything else by itself. It's very doable.