how to maximise windows in mountain lion like windows 7? In Windows 7 you can stretch the window to whole screen by holding the window at top edge and dragging it to the top edge of screen

You can also stretch it half of the screen size and align it to the respective side by holding the window at top edge and dragging it to the left or right edge of screen

how to do this in mountain lion?
No default option aside from the fullscreen button in the top right corner of some applications. The three colored buttons in the top left of windows also give you some control.

However, there are third party tools available. I found them because I love the snap feature. After trying out a few, I settled on BetterSnapTool because it was the simplest to use and had the most features. Set it to start on bootup and you're all set. I love it.

I don't remember if I bought it in the Mac Appstore or from their website, but the link above is a download from CNet.

Hope this helps. Good luck.