It is Wizards of the Coast and they are selling high quality scans of the old classic books. (So not free.)

It is WoTC's own store, so it fully legal.

I believe it's being put up by wizards of the coast. They've been working on it for a while. So I think it's totally legal.

Brutally speaking, the fact that it's down speaks to it's authenticity as a WotC site. :) They have had horrible luck with partners for their online apps, such as the character builder and online tabletop.