KeePassXC Responds to ProtonMail's Encryption Claims for Password Manager
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The only other stack I've used is on-premises Bitwarden for small businesses, because it provides a more flexible multi-user permissions model. That can be made fully self-hosted and open source by using Vaultwarden for the server.
I don't see any advantages to using Proton Pass over those, frankly.
They are in the business of trust.