Ask HN: What successful startups started as "Show HN"?

I thought pulling together a list of startups who've done this would be interesting, to explore and perhaps better document the influence of HN on the startup community. We'll count both stand-alone startups who used Show HN in their launch / iterating strategy and side projects that have evolved into stand-alone startups, for the sake of discussion.

Also, if your startup has gone through this: how do you feel using Show HN as a means of launching / gathering feedback my have helped or hurt your product?