Percona Server for MySQL
Drop-in MySQL replacement. Percona, 2006. Peter Zaitsev (ex-MySQL AB performance team). Same binary API, more features + better tooling.
Adds: XtraDB (improved InnoDB), Percona Toolkit (online schema changes, pt-online-schema-change), XtraBackup (hot backup), better Performance Schema, audit logging. Pricing: open source GPL + paid support. Competitor: MariaDB (another MySQL fork), Oracle MySQL Enterprise. AWS Aurora MySQL is the cloud-only alternative. Modern development: Percona Operator for Kubernetes, Percona Monitoring + Management (PMM) tool. Strong in hosting providers wanting extra MySQL features without paying Oracle.