Sure, Saxon-B is open source and provides the whole of XSLT 2.0 except for schema-aware processing. (Schema-aware processing is offered by Saxon-SA, the "commercial" version of the product).
Saxon-B 8.3 can be downloaded by following links from
http://saxon.sf.net/
Michael Kay
http://www.saxonica.com/
Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference