A few of the folks at one of the other sites got tired of database errors, extended downtime, and other (lack of) functionality that made the other site, generally unusable.
These people have started Model Insider.
I’m there. A bunch of other wonderful people are there. The official launch is February, as there are a few other areas of the site that need to be worked on, but the site launch was pushed forward by a few unfortunate events at the other site.
So far, I’m a huge fan!