There was one great art exhibition in my town, called MINI - ART scena held around Christmas time.
Only rule was format of the art work, 10x10 cm.
All works were for sale and people used to come and buy Christmas gifts in form of painting, small sculptures or some pottery. I believe it lasted almost for twenty years.
I have participated in few of them and here is my favorite work made for on of them.
oil on canvas
10x10 cm