What is the WSS Certificate Web Service?
I found that on Windows Server 2012 Essentials it was installed automagically. I've stopped the site for now, but would like to know why its there.
In this context, "WSS" stands for "Windows Server Solutions," which is the platform name for the Small Business/Essentials versions of Windows server. So, "WSS Certificate Web Service" would be "Windows Server Solutions Certificate Web Service."
So, it's a web server that serves certificates for the Windows Server Solutions platform.
This service is used to allow certificate-based authentication for remote connections to the server that require certificate-based authentication. It's a web service because Microsoft made a design decision in this line of products to expose their APIs over a web service where possible, presumably in the interests of making them easier to work with, which would make sense given the target market of this product line.