What are some alternatives?
Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
MyPaint - MyPaint is a fast, distraction-free, and easy painting tool for digital artists.
Adobe Illustrator CC - Adobe Illustrator CC is a commercial vector graphics editor.
JugiPaint - JugiPaint is a painting software with diverse tools for various types of illustration work.
Sketch - Professional digital design for Mac.
Leonardo - We believe artists deserve the best possible tools and we are determined to give it to them.