Google Chrome desktop browser and Chrome for Android include now support for WebRTC (Web Real Time Communications), an emerging web standard that helps  real-time audio and video capabilities to their web applications without the need for plug-ins or proprietary codecs.
There are various  apps has capabilities like voice calling, audio & video conferencing, video broadcasting, screencasting and screen sharing in the browser via simple JavaScript without requiring plugins.

Some of  web apps are like http://same.io,http://talky.io http://appear.in to Video /Voice chat Screen sharing without  installation or download anything. Only you require is the latest Chrome browser.

There’s a little setting in Chrome that you need to enable . Type chrome://flags in your Chrome’s address bar, find the setting that says “Enable screen capture support in getUserMedia()”, click the Enable button and restart your Chrome browser.