What is Vaultwarden?
Bitwarden is a popular commercial password manager. It's been audited for security and is zero-knowledge to the server operator, with all decryption being handled by the client using a master password. The advantage of encrypted data being stored on a server is that you can access and update your password vault from multiple devices, with updates being immediately available on all your other devices.
Bitwarden is available as a free product and in a paid version that provides additional features, like integrated 2FA authenticator (TOTP) functionality, the ability to create "organizations" where passwords are available to multiple users, security reports that notify you of reused and potentially vulnerable passwords, and much more.
Vaultwarden is an open-source implementation of the Bitwarden server, written in Rust, that provides nearly all of the paid Bitwarden features for free. It provides the same zero-knowledge security guarantees as Bitwarden, and works with the official Bitwarden clients. We strongly recommend using the official Bitwarden clients because they are open source and have been subjected to thorough third-party security audits.