Note: I have rewritten this article after crtitics which was deserved a bit:-)
To whom it may concern.. This is still a bit naming mess. The two pieces of software have almost nothing to to do with each other.
“Mapserver Enterprise” simply does’n exist anymore and is now called MapGuide Open Source, open source approach to web mapping, based on original Autodesk’s code. Despite of the former name, there is no “child” version of UMN Mapserver nor fork, there’s one Mapserver. A bit of history – Autodesk entered in free GIS in 2005 with its MapGuide. As they were publishing a huge amount of code I think that they wanted to make it a big way. They invented these two names, but there was little response for calling Mapserver other names.. Now, the name “Mapserver Enterprise” is not promoted anymore and the product resides on http://mapguide.osgeo.org/. Anyway, some people from Autodesk still call it so – I have heard it recently on GlobalGeo in Barcelona. But it is probably only a mistake – Mapserver Enterprise simply doesn’t exist anymore.
MapGuide is not written in Java as I originally thougt, but “entirely coded in cross-platform C++, using SWIG to generate the user-facing web APIs” (citing Jason Birch) and has some quite interesting features – i.e. using DXF vector plugin in browser, extensive ajax use etc. This comparing to old unix-like C/C++ mapserver may appear really to be anvaced edition. I certainly think that != true; Everybody can choose the best for his needs – oh wait there is already Geoserver! Cool J2EE app built with GeoTools.