Bitwarden Authenticator is a standalone app that is available for everyone, even non-Bitwarden customers.
In its current release, Bitwarden Authenticator generates time-based one-time passwords (TOTP) for users who want to add an extra layer of 2FA security to their logins.
There is a comprehensive roadmap planned with additional functionality.
Available for iOS and Android
Because you can enable totp on your Bitwarden account and it would be dumb to store the password and totp for your biwarden vault in your vault?
Also it can act as a stepping stone for non Bitwarden customers, before getting their own vault.