MariaDB

MariaDB is a solid MySQL-compatible database that's served well for years. It's reliable, well-understood, and has good tooling. The reason it's on Hold rather than Adopt is simple: PostgreSQL does everything MariaDB does and more.

JSONB, full-text search, CTEs, window functions, and extensions like pgvector give PostgreSQL capabilities that MariaDB lacks or implements less elegantly. For existing MariaDB applications, there's no urgency to migrate. For new projects, PostgreSQL is the stronger starting point.