Happy Fifth Birthday XSLT!
Altova GmbH has released the Altova XSLT 1.0 and 2.0 Engines and the Altova XQuery Engine. These are closed source and free-beer products for Windows 2000 and later. These are the same engines used in XMLSpy. The XQuery and XSLT 2.0 engines are not fully standards conformant. I'm not sure about the XSLT 1.0 engiune, but any bugs in XMLSpy's XSLT are probably found here too.