A sort of combination of Hindi and Urdu (AFAIK as an attempt to unite the Hindu and Muslim populations). Here's some history:
http://www.hindu.com/thehindu/mag/2004/01/18/stories/2004011800040300.htm http://www.languageinindia.com/april2005/earlygandhi1.html http://en.wikipedia.org/wiki/Hindustani_language
Of course it does not address the misgivings of the South where Hindi (or Hindustani) is not widely spoken. As mentioned earlier, the imposition of Hindi in Tamil Nadu was met with widespread protests and rioting.
--ravi