Firebird

Firebird is a relational database offering many ANSI SQL standard features that runs on Linux, Windows, and a variety of Unix platforms. Firebird offers excellent concurrency, high performance, and powerful language support for stored procedures and triggers.

Firebird is a fully featured and powerful RDBMS. It can handle databases from just a few KB to many Gigabytes with good performance and almost free of maintenance!

Below is a list of some of the Firebird's major features:

Full support of Stored Procedures and Triggers
Full ACID compliant transactions
Referential Integrity
Multi Generational Architecture
Very small footprint
Fully featured internal language for Stored Procedures and Triggers (PSQL)
Support for External Functions (UDFs)
Little or no need for specialized DBAs
Almost no configuration needed
Large user community
Optional single file embedded version
Dozens of third party tools
Careful writes - fast recovery, no need for transaction logs!
Many ways to access your database
Native support for all major operating systems
Incremental Backups
64bits builds available
Full cursor implementation in PSQL
Monitoring tables
Connection and Transaction Triggers
Temporary Tables