Apple and World Wildlife Fund have collaborated with Apps for Earth. Until April 24th 2016 all proceeds of the 27 apps will go to World Wildlife Fund. Procreate, my favorite drawing and painting app for iPad, is also part of the Apps for Earth Project.
They have teamed up with Kyle T. Webster, an illustrator and developer of brushes for Photoshop. He has made 8 natural brushes for Procreate that are now available as an in-app-purchase.
All the proceeds of the brushes go to WWF. I have bought the brushes and tried them out on some landscape paintings. They are great brushes with nice structures. They are great to paint grass, rocks and other natural phenomena. So if you have Procreate or an iPad and want the best drawing app, go the Appstore and by the app and support WWF.