I've been researching the new "bounty platforms" paradigm recently that seem to be multiplying, though most of them don't seem to be any good.
The only one I would recommend is the first one in this list, though it can feel a bit slow to begin with, it's functional at least and has active campaigns.
bountyhub.io - still in beta testing, relatively new but growing fast in popularity (also has bounty for it's own tokens)
bounty0x.io - the one that everyone seems to know and is the most popular, but it's for all bounties (although blocked by forum)
bountiesalert.com - this is the sister website of airdropalerts.com and quite reliable (though not a platform for bounties)
bountyhive.io - relatively popular but rarely seems to have any available campaigns so at the same time relatively useless (blocked by forum)
bountyplatform.io - haven't tried this one properly yet as there are currently no available bounties on the platform (also blocked by forum)
bountyportals.com - haven't tried this either as the current/previous campaigns appear to be worthless $ value
bountyhunters.io - i think this died as a platform, there are no tasks/campaigns available anymore (if there were any in the first place!)
There are probably some more but these are the main ones that are up and "running" at the moment. any other lists appreciated though!