Microsoft essentially invented AJAX. In the late 90s they had some HTML remote update thingy via a Java applet, I believe. Then they introduced XMLHttpRequest. Developing for IE around that timeframe wasn't bad. They had excellent documentation, and added (proprietary, sure) extensions that let you do all sorts of neat stuff.
Yes. Microsoft invented XMLHTTP so they could build a killer web client for Exchange Email. Remember when you first saw that? It was amazing. IE 5 was hands down a more capable browser than any other when it was current. It was nonstandard, but it was very productive. You could do AJAX, XML to HTML transforms in the browser with XSLT, xpath navigation of XML documents, etc. JSON wasn't popular then but support for XML was excellent.
They didn't have the vision to build consumer oriented "cloud" software like Google did, but they were positioned to do it before anyone else was.
MS ran off the hell off of Xenix internally. Mail, calendaring, etc. I remember when NT was going to be the best Unix out there... And then Win32 happened and coolaid got sloshed around. The NT Kernel could have been an amazing Unix.