Apple has this; it's called iCloud keychain.
- Mainstream GNU/Linux DEs: Gnome Keyring and KDE KWallet (both implement common XDG API)
- Android: Smart Lock Passwords
Neither is interoperable with each other, at least not without external tools (I'm unaware if those exist). I wrote a comment about it the other day: https://news.ycombinator.com/item?id=15697011 (it was about syncing passwords across browsers)
If my interpretation is correct, then I think I need to be the cliche bearer for the XKCD reference: https://xkcd.com/927/
If your interpretation is correct then yeah, Apple has Keychain.
Also, I think I recently got an OS-level 'save password' prompt for something recently on my machine running Win10 Pro v1709... Can anyone confirm or refute this?[1] No clue if this is just a new skin for the existing Credential Manager, something new entirely, or just confusion on my part.
[1] I just now tried Googling for information about this, but I nearly drowned in the sea of links about IE password saving and Edge support for password manager plugins
For local keychains there is /usr/bin/security, but it does not see iCloud keychains.