I've looked into it a little but not much for don't have the need now. But there are a few options out there. Others may know the details.
This is one I have looked at that seems to be very popular now.
http://eaccelerator.net
Could come in handy if you have allot of active php scripts running with allot of activity like forums, galleries and such.
And the VPS dose have the cPanel and WHM control panels with all their goodies if that is what you were asking about as far as "software installed".
You may find this informative also.
http://meta.wikimedia.org/wiki/PHP_c...d_optimization