MapWindow 6 is completely separate and independent from MapWindow 4. MapWindow 6 is entirely in C#, has no active X control or com library components, and features advanced symbology sets. It is still in beta, but already has most of the features needed for many successful .Net GIS systems. MapWindow 6 is officially moved to:
http://mapwindow6.codeplex.com/




Hydrodesktop is designed with the time series needs of hydrology in mind. It builds on the new MapWindow 6 foundation, but extends it with specialized support for downloading and analyzing hydrologic datasets
http://hydrodesktop.codeplex.com/




MapWindow 4 is a free windows GIS application and uses an ActiveX control at it's core that can be embedded into many applications that don't support .Net such as excel, access, visual basic 6, or other pre-.Net languages.
http://www.mapwindow.org