UPDATE 5/27/19: Looks like these features are no longer available.
Flickr has something called “interestingness.” I don’t know if this is new or I just never noticed. A photo gets included based on “where the click-throughs are coming from; who comments on it and when; who marks it as a favorite; its tags” and other stuff. You can spend hours on interestingness so don’t go unless you have some time.
Not sure why, but there’s a calendar view in case you wanted to see interesting photos from June, 2008, for example.





