Offline XSLT processor

If you need an off-line XSLT processor, nothing beats SAXON. It supports XSLT 1.0 and XSLT 2.0 and the lower-end version is free. I am strictly using the 1.0-only version to ensure my code is compliant with major browsers, but you might want to get the 2.0-version for special projects.

I'm primarily using SAXON to test my XSLT code (or develop new programming techniques) before deploying it in a distributed environment. I was also using it to develop the WordML transformations that are now executed within the context of Save As ... function in Word.