Firebird is an open-source SQL relational database management system that support Linux, Microsoft Windows, macOS and other Unix platforms. The database forked from Borland's open source edition of InterBase in 2000 but the code has been largely rewritten since Firebird 1.5.
Firebird is ACID-compliant (atomicity, consistency, isolation, durability). ACID is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps.
Firebird has many access methods: native/API, dbExpress/FireDAC drivers, ODBC, OLE DB, .NET provider, JDBC native type 4 driver, Python module, PHP, Perl
Firebird supports External Functions - a mechanism for extending the functionality of the database server by adding a function, that can be evaluated in standard query language statements.
Improved multithreading, regular expression syntax and the ability to query remote databases