Universal I think all apps should have a tip feature. (I know what your thinking)

[max2]

Even the free ones.

I recently tipped a app developer and they fixed their app for me a few days later. Awesome.

 

[pacorob]

I agree with you there max especially the ones that actually offer a great app and deserve offer e.g. a great service, game and do offer the option to remove ads, no in-app purchases for gems/coins but only have options to remove ads and support developer to stay alive in the App Store for a long time and maintained with updates!