You can download app and be awarded gem's of differing amounts for the completion of various requirements, I am currently owed 700+ gem's for doing the requirements of a few of these. I have not received any of the gem's despite both TapJoy who run that and Ubisoft who allow them to do so both of them know that there is a issue surrounding the non reward of these gem's they don't tell you until you speak to representatives of Ubisoft Mobile team then inform you that there is no ETA on a fix.