PaintMIXER by developer Gefa is a homebrew application for the PSP. This is great for the artsy type of person, who enjoy a good drawing board on the go.
Latest version at this time is 2.3.0. If you have ever used Window's Microsoft Paint (MS Paint), then you will be familiar to this application as it is a clone of it.
Personally I have not tried it, although I am an artist and use many graphical softwares on my computer. I am thinking about installing this to my PSP and adding my experience to this post.
In the meantime I love to hear comments from those who have tried it, or know of other graphical design applications to the PSP, reply by commenting this post. thanks :)