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
WhiteBear is a set of foundation classes for database engines written in Java. It supports object and relational database, is highly portable and may be used in embedded or server environment. Project has been created from scratch and plan to includes storage engine, server, SQL interpreter, ODBC, JDBC and JDO interface
BearDB is a database provider for modern web applications and javascript frameworks.
BearDB is our Relational Database System which runs on most platforms and supports multiple programming languages. A REST server allows web applications to go directly to the database.
BigBear is our Large Scale Database System which supports SQL. BigBear is similar to modern distributed NoSQL database systems, with the addition of support for SQL and a REST server.