AngelList is a platform for startups to meet investors, candidates and incubators. It was started in Jan 2010 by Babak Nivi and Naval Ravikant, who also write Venture Hacks.
The AngelList team and a rotating group of analysts from the top VC firms in the world reviews startups after they are published and features interesting companies to investors. This usually happens no later than 72 hours after the startup profile is published. This review is very similar to one that would be conducted by a venture investor, considering product, team and traction.
Startups can only accept money from accredited investors whether they raise money publicly or not. However, startups that raise publicly are required to verify that each of their investors is accredited. If a startup that raised publicly closes their round on AngelList (via syndicates), AngelList will handle all 506c investor verification.
On AngelList all the investors have stated that they are accredited. The vast majority of the investors have also made several angel investments.