I have a donation button on some of my free apps, i just only received 1 donation from an user in more than 3 years, then i offered an InAppPurchase that gives: unlockable premium content + no ads, i received 9999% more revenue with this strategy.
I think we also need to know how to sell or generate profit with our work. you can offer a free app, we can give the user the posibility to have more features, if the user likes your app, will like more if he can have more PREMIUM or EXTRA content/features for a small amount.
Sorry my bad english.
Regards.
Apart from programming languages, I can only speak English. I am trying to learn French, but this would have been much easier when I was younger. "Your English is Very Good".
Thanks for your feedback regarding Donate buttons and In-App-Purchases.
This information and comparison is what I was looking for.