At the moment Reactor supports the following Database Management Systems:
Microsoft SQL Server – Reactor is known to support Microsoft SQL 2000 and 2005 servers. The Express edition of SQL Server 2005 is untested, but should work too.
MySQL 4.x – Reactor supports MySQL 4. One consideration to keep in mind is that views are not supported in MySQL 4.
MySQL 5.x – Reactor supports MySQL 5 completely.
DB2 - Reactor has been shown to work with DB2 express edition.
Oracle - Reactor works Oracle 9i and 10g. Reactor does not support Oracle 8i, though this may be added in the future.
Oracle RDB - There is also an adaptor for working with Oracle RDB, though this is not supported nor officially tested.
PostgreSQL 8 - Reactor works with Postgres 8. It is untested with earlier versions.