Most sketching apps on the market focus on single projects and their underlying layers, rather than a canvas of ideas and suggestions. Forge is different.
I've long thought the iPad was perfect for rough storyboarding: It's not an artist's preferred medium for detail work, but it's portable, and easy to sketch on, and has plenty of storage space. Forge, built by the folks behind the Jot Touch stylus, invites you to explore a hundred different ideas and sketches in storyboard format, iterating and trashing and reinventing as you go. I've been testing Forge for months, and it's become one of my go-to tools for planning and messing around with creative ideas.