FreeTDS is an open source implementation of the TDS (Tabular DataStream) protocol used by these databases for their own clients. It supports many different flavors of the protocol and supports several APIs to access it. Additionally FreeTDS works with other software such as Perl and PHP, providing access from those languages as well. There is also a native (type 4) JDBC driver available for platform-independent Java clients (including Java Server Pages applications), with support for most of the JDBC 1 API and portions of the JDBC 2 API.

WWW: http://www.freetds.org/
