libxslt is a very efficient XSLT 1.0 processor and is usually included in every recent Linux distribution (packaged under the name libxslt or xsltproc). On Microsoft Windows, binaries are packaged along with Nectil.

Nectil tries to use this processor on command line unless the Sablotron PHP extension is installed. Nevertheless we encourage the use of libxslt over Sablotron, because it's more standard compliant, faster, easier to install.

libxslt might endure some instabilities on Microsoft Windows, unexpectedly hanging and requiring a complete restart of IIS.
If you observe these kind of behaviours, try to switch to SaxonSaxon, which doesn't have these problems.