This was more than a rumored project. Infoworld posted stuff in this article: http://www.infoworld.com/articles/hn/xml/99/10/25/991025hnmicrosoft.xml.

My understanding of all this is that COOL was an initial project within MS. Then, the idea morphed into something grander. Why have one language with all these great features when you can develop a runtime with them and let developers use many languages? COOL moved from being a language to a way of doing things at MS. My guess is that we've heard of it under 4 different names: COOL, DNA, NGWS, .Net. The grand idea became CLR, IL, C#, VB 7, Eiffel#, etc.

You can even see this quote from Greg Leake (attributed as a Visual Studio
PM) at: http://www.infoworld.com/cgi-bin/displayArchive.pl?/99/07/t02-07.1.htm.

-- sg