Free drawing software?

I am an artist by no stretch of the imagination. I like to diddle around in MS paint, but I was hoping to improve my art and drawing skills. I have no intention of being a professional or ever really benefiting from art, I just want to get better. I don't want to go out and spend $100 on art software so I'm hoping to download some fun little art program online. Do you have any recommendations of a free novice friendly basic art program?