What graphics software did Otis from the gadget show use when he made his own T-Shirt designs?

GIMP is the closest thing to Photoshop you will find. Its actually a really great free open source program, and if you are familiar with Photo shop you will get use to this program very quickly. Its really great if you like to use patches the sources are endless because so many people are creating their won. Check them out, I use that and photoshop for my own T-shirt desings. Check out my work at www.cafepress.com/dirtyanthem