Appwrite

Appwrite positions itself as the backend for any platform — and it takes that commitment seriously. A single Appwrite deployment exposes authentication (with 30+ OAuth providers, team membership, roles, and label-based permissions), multiple independent databases per project using a collection-and-document model, object storage with built-in image transformation and anti-virus scanning, cloud functions across 11+ runtime environments, and a messaging API for push notifications, email, and SMS. Most competing BaaS platforms treat push messaging as a third-party integration; Appwrite ships it as a first-class service.

The SDK story is equally broad. Web, Flutter, iOS, Android, and React Native all get official SDKs that expose the same concepts in the same order, so a developer switching from mobile to web finds the API immediately familiar. Realtime subscriptions fire across databases, storage, and function events through a single WebSocket connection, which simplifies client code that needs to listen to activity across multiple service layers.

Self-hosting runs via Docker Compose and is well documented. The community edition is BSD-3-licensed and free; Appwrite Cloud is the managed alternative with a free tier and growth plans. The document database model means there are no SQL joins or foreign-key constraints, which can be a limitation for complex relational data. The managed cloud is newer and covers fewer global regions than Supabase's offering.

For developers building cross-platform apps who need databases, auth, storage, functions, and messaging under one consistent API without stitching together separate vendors, Appwrite is a strong candidate.