What is Firebird ?
Free open source relational database (no double licensing) for Windows/Linux/MacOS/Android, with drivers for JDBC, .NET, Node.JS, Delphi, PHP, Python, etc. Highly scalable (from embedded to 1000+ connections), compact (Windows installer is 7Mb), in repositories of major Linux distros. Easy installation: runs out-of-the-box; easy maintenance: incremental and full online backups, self-maintenance; enterprise features: database and wire encryption, trace/audit, autonomous transactions, monitoring.