Can't really say about apps but Zostel, GoStops and Hosteller are great Backpacking hostels. For apps, checkout Hostelworld, Couchsurfing and Worldpacker. Cheers!
You can try 1 , airbnb homestays 2. make my trip homestays 3. hostellers (they are really good) its not an app its a website ,
4.Zostel (they are also really good)
Hands down for booking.com...I used that for Vietnam and Cambodia trips...worked efficiently and reasonable rates..Used the same for Mangalore stay as well...