Microsoft have announced their proposal to bring realtime communication in browsers, all without plug-ins. The W3C WebRTC working group received "Customizable, Ubiquitous Real Time Communications over the Web" (CU-RTC-Web) proposal from Microsoft, which is the first step toward creating a standard that would be key in creating a browser-based version of Microsoft's expensive acquisition, Skype.
Other companies have already laid out their plans for HTML5-based communications, with Google and Mozilla already doing so. Microsoft, on the other hand, are waiting to make it publicly available until it's a fully formalized standard. Stopping the software giant right now is the choice of codecs being used, with Google and Mozilla wanting to use the open sources VP8 as default, with Microsoft wanting to be more flexible.
Outlook.com is getting eyed at by Microsoft to get some Skype integration, which is something the company has been planning for quite a while now. This would require a plug-in and would not use WebRTC, but it could change somewhere down the line when the standard is complete. The WebRTC standard would allow cross-platform audio- and video-based communications, potentially allowing services such as Google Talk and Skype to work together.