Cool as in "geek cool" or as in "general cool"? As in "geek cool", there were many. Even Windows for Workgroups was cool because it offered Mac-like networking for PCs. MS Access was cool. Even VB was cool (before it a Windows hello world was 100+ lines). My Softcard was cool - it allowed my Apple II to run CP/M programs. Microsoft's mice, keyboards and joysticks were always top-notch.

As in "general cool", I can't remember a single one. Perhaps the Xbox 360 makes the cut, but only in the 25+ gamer scene.

There would also be some "fashion-victim cool": those who just need the latest shiny toy. Those were the ones who jumped into Vista, Office 2007 and then to 7 and 2010 just because there is a newer version, disregarding whatever feature they needed. Obviously, they are not restricted to the Microsoft space - and I have pushed my PPC iMac well beyond its last supported OSX version (the G3 runs 10.4, but is not very snappy). These people also swap hardware like crazy, often having 8-core, 64-bit desktops where they check their hotmail accounts and zip through Facebook at speeds unheard of.