nepeter:

have you tried mypaint?

• its free
• its open source
• works for windows, linux and mac
• 90% of the window space is where you draw, no clunky and messed up menus
• performance-wise
• supports layers
• the canvas is basically unlimited, the program automatically chooses a dimension for your picture when you save
• easy (but not too limited) brush creation
• overall fucking awesome

obligatory screenshot