ArtFlow is a very nice app with all the features added on two vanishing sidebars. It has over 70 brushes including a smudge brush. The brushes are pencils, airbrushes, pens, paintbrush, watercolor, special shapes, texture brush, and smudge brush. Each brush category has several variations and you can also adjust each variation. I don't think you can save customized brushes in this app, but it will remember your last settings. This app supports layers and layer functions such as multiply, overlay, glow, lighten, darken, and several others. You can also import photos and add effects such as sepia, vignette, and adjust the brightness and saturation. The canvas size goes up to 4096 by 4096 pixels. ArtFlow also has a paint bucket tool, a symmetry tool, guides, and geometrical line shapes. It also has a custom color palette that will float on the screen. This app is especially designed for tablets and runs in landscape mode. I really like this app because it has a very nice user interface. I did notice a little bit of lag when using the smudge brush. The UI vanishes when you draw and you can bring it up by tapping on the arrows on the sides.
ArtFlow UI with side panels closed.
ArtFlow UI with both side panels and brushes menu open and floating palette.
I did this painting in ArtFlow as a lesson on how to paint snow at http://wizzley.com/authors/EllieTaylorArtist/