Firebird RDBMS offers ANSI SQL features & runs on Linux, Windows & several Unix platforms. Features excellent concurrency & performance & powerful stored procedure & trigger language.
More information and downloads at https://firebirdsql.org/, issue tracker is https://github.com/FirebirdSQL/firebird/issues
Sedna is a native full-featured XML database management system.
Sedna is a free native XML database which provides a full range of core database services - persistent storage, ACID transactions, security, indices, hot backup. Flexible XML processing facilities include W3C XQuery implementation, tight integration of XQuery with full-text search facilities and a node-level update language.
Easy to use web-based database management system. Functionally equivalent to a simplified version of Microsoft Access. Written primarily in PHP using the MySQL database engine. Supports all platforms that PHP/MySQL supports: Linux, Unix, Windows.
JMigre is a 'universal' databases convertor based on Java and JDBC.
It should be able to convert any database from any database management system (DBMS) supporting JDBC, to another DBMS supporting JDBC (on any OperatingSystem supporting Java).
Deploy in 115+ regions with the modern database for every enterprise.
MongoDB Atlas gives you the freedom to build and run modern applications anywhere—across AWS, Azure, and Google Cloud. With global availability in over 115 regions, Atlas lets you deploy close to your users, meet compliance needs, and scale with confidence across any geography.