It's an android app from Google that has very short (3-4 questions) surveys anywhere from a couple times a week to a couple times a day. Each one pays anywhere from $0.10 to $1.00 (the majority are $0.10-0.25). The money is in Google Play credit so it works great for small purchases like the monthly diamonds.
As a caveat, It's not available in all countries and the number of surveys you get can depend on your location, demographic, etc.
https://play.google.com/store/apps/details?id=com.google.android.apps.paidtasks