Rapid PSD was a service that turned a Photoshop file into markup. You uploaded a PSD, gave it your email address, and the XHTML and CSS came back to you.
Three steps on the front page, which was the whole pitch: upload your file, wait for your email, enjoy your html.
The conversion was automated. A script took the PSD apart and generated the markup from it, which is why the promise could be "wait for your email" rather than "wait a few days" — there was nobody in the middle doing it by hand. The site itself was ASP.NET.
It went live and it never really went anywhere. That's most of what there is to say about it commercially, and it's the common ending for this sort of thing: the build was the interesting part and the business wasn't.
The part worth noticing is what came next. Three years later I built Psd2Html, which did the same job as a macOS app, and the line I wrote about it then was that no data ever left your mac. That's not an incidental feature. It's the answer to the obvious objection to Rapid PSD, which was that doing this as a service means handing your unreleased design to a stranger's server and hoping.
The same problem, solved twice, four years apart, and the second answer was mostly about where the work happened rather than how.