Are there any rapid (low fidelity) wireframing/prototyping tools for webapps on the iPad?

I use two tools – the aforementioned Omnigraffle (which is really great and supports any of the template libraries that are available for the desktop version, so you can use it to mockup anything) and iMockups, which is basically Balsamiq for the iPad – it even imports and outputs balsamic projects. I also use Blueprint but it is targeted at mocking up iOs apps, and is not very flexible beyond that.

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