Backend-as-a-service platforms handle auth, database, and storage so you don't build them from scratch. Supabase (Postgres, open-source) and Firebase (Google, NoSQL) are the two leading all-in-one options. Railway and Retool round out the category for general app hosting and internal tools respectively, while Clerk specializes specifically in authentication if you want to mix and match rather than use an all-in-one platform.