Firestore is a document database from Google Cloud. A document database stores each record as a JSON-like document, grouped in collections, instead of as a row in a fixed table. Firestore is fully managed and serverless: Google runs the servers and scales the database up and down, with no manual sharding (splitting data across machines) and no maintenance windows.
Mobile, web and server apps read and write documents through client libraries. Real-time synchronization sends changes to connected clients, and offline handling lets an app keep working without a network. Queries can use indexes, full-text search, geospatial filters and vector search, and ACID transactions can change several documents at once. Access control works with Cloud Identity and Access Management and Firebase Authentication. Multi-region replication keeps copies in several regions with strong consistency, under a 99.999% availability SLA. A MongoDB-compatible API lets existing MongoDB code and drivers use Firestore.
Firestore is pay per use: it charges for each document read, write and delete, for stored data and for network traffic, with a free daily quota for one database per project. It comes in a Standard and an Enterprise edition.