Vaultwarden is a lightweight, open-source reimplementation of the Bitwarden server written in Rust. It is fully compatible with all official Bitwarden clients (browser extensions, desktop apps, iOS, Android) and runs on hardware as modest as a Raspberry Pi using under 50 MB of RAM. This guide covers everything: what Vaultwarden is and how it compares to Bitwarden and 1Password, Docker installation, why HTTPS is mandatory and how to solve it without a domain using Localtonet, the correct way to generate the ADMIN_TOKEN with Argon2, how to disable open registration, connecting Bitwarden clients, a complete backup strategy, Fail2Ban brute-force protection, and a dedicated Raspberry Pi section.