e621: Among those Booru-type boards which are predominantly furry-themed, e621 is one of the larger ones. It is paid for by Varka of Bad Dragon, who also pays for AGNPH, and one of its lead administrators is retired AGNPH admin Psyco Charmander.
Char has retired from e621, actually.
Your information on e621 is not accurate. e621 is paid for by Dragonfruit Ventures LLC. Varka does have his hand in it though.The reason e621 is compared to the new software is because they both run Ouroboros, a proprietary Danbooru branch.