BorgBase is a hosted backup service for Borg and Restic repositories. You manage repositories through a web interface or an API, and the service provides monitoring and alerts for stale backups by email, Pushover or webhook, an append-only mode, server-side compaction, TOTP two-factor authentication and copy-paste setup commands. According to the vendor, data is encrypted on your machine before upload, BorgBase does not hold your repository password and it cannot read your backup contents. It is delivered as a cloud service for individuals and organisations that already use these open-source backup tools.
BorgBase is operated by Peakford Ltd, based in Naxxar, Malta, an EU member state. For each repository you choose between EU and US regions, so selecting an EU region keeps that repository's data in Europe. BorgBase itself is not open source, but it supports open-source backup projects such as Borg and Borgmatic and develops the Vorta client. Because the repositories are encrypted client-side, the service holds only ciphertext, and you can move to another host that supports Borg.