Tech Writing 2.0 - The impact of Web 2.0 on technical illustration

Last week we said:

"At the moment, the biggest problem is how to tag particular areas of a diagram (to be called "segmented tagging" or "hotspot tagging" perhaps?), but that's unlikely to be a showstopper."

And this week, a Web site went into service that solves this problem!
Does anyone else know what that Web site is ?
A clue - It's a four letter word beginning with R.