XT on Unix platform
Yes, you have to install java first though.
XSL on Unix systems
As far as I know, most XSL engines are written in Java, so you should not have any trouble finding a good one if you have a Java Virtual Machine installed. You can easily get one from http://java.sun.com . You might try www.jclark.com/xml/xt.html for XT, which is a popular and good XSL engine. There are several others. Also see Apache Cocoon : http://xml.apache.org/cocoon