Can anyone recommend simple user interface design software?

I seem to remember a startup recently linked on this site that solved my exact problem, but for the life of me I can't find it and Google is no help.

I am looking for simple software (preferably destop) that lets me mock up user interfaces quickly. The software I recall actually had working widgets and would serve nicely for basic 'does it work right' logic.

Am I imagining things or does such software actually exist? If so what is it and why is it so hard to find?

You're thinking of Balsamiq Mockups - or, if you're looking for one to mock up desktop applications (and aren't opposed to using software from the Evil Empre), Viso.

the seo is not that weak, but the name is odd... spelled with a q instead: balsamiq