Similarity between EPiServer CMS and WSS
Having worked on EPiServer CMS and WSS I tend to compare both the technology. Both the CMS are made on .net so it is natural that they share similar feature. One of them is a VPP.
.Net framework 2.0 introduced a class called Virtual Path provider.
In EPiServer CMS it is used to hold the static files. The files are saved within the system folder and a virtual file system is created using VPP class. It acts as an interface between base file system and the CMS users.
In WSS VPP class is used for URL rewriting. WSS has its own version http application/http modules where it uses the VPP class.
Similarly there are many more features shared between EPi Server and WSS.