PlanetScale is a cloud database hosting service made by PlanetScale, Inc. It offers three products: Vitess, a MySQL-compatible database system with horizontal sharding (splitting one database across many servers); Neki, sharded Postgres; and PlanetScale Postgres. The home page says the founders of PlanetScale developed Vitess at YouTube, and PlanetScale now maintains it.
Databases run on network-attached storage or on PlanetScale Metal, which uses local NVMe drives. Shared features include branching (isolated copies of a database for safe development), read replicas, a high-availability setup with one primary and two replicas in three availability zones with automatic failover, built-in connection pooling, automated backups and Query Insights for monitoring. Vitess adds deploy requests: schema changes that a team reviews and that run with no downtime. PlanetScale Postgres adds point-in-time recovery and curated extensions such as pg_cron and TimescaleDB.
PlanetScale is a hosted service billed month to month by resources: instance size, shards, replicas, storage and network use. On the Enterprise plan it can also run inside the customer's own AWS or Google Cloud account.