I know that the Office Ribbon has gone under pretty significant changes since 2003 and I've done some modest customization of the ribbon in 2010.
Question: I've seen a number of references to .Net and specifically C# and the Office Ribbon. Is this largely just (maybe) dynamic customizing? I mean, Office 2013 can't run any .Net code, can it? At the end of the day, it is still VBA no?
Best How To :
I imagine that you are referring to the Ribbon WPF control, documented here: https://msdn.microsoft.com/en-us/library/ff799534%28v=vs.110%29.aspx
This is a UI control that can be used in custom .NET applications, giving them the look and feel of office applications.
If you are referring to the ribbon in actual office applications- as the comments mention, addins can be written in .NET code (this has been possible for quite some time, actually), and these can modify the toolbar. Links are available at the bottom of the page linked above.