A lot of people don’t like either the Republican or the Democratic candidate. Many people believe politics has gotten too extreme and want to vote for a centrist. Quite a few people are sick of so much partisanship, believing that our hard times call for a national unity slate. Lots of people believe our political system, with its caucuses and in-person rubber-stamping conventions, is antiquated and that the internet holds promise for greater participation in our democracy.
So Americans Elect was formed, with substantial backing, and gained ballot access in half the states. Ordinary Americans would choose the candidates in a virtual convention. The Presidential and Vice-presidential candidates would have to be from different parties. (Thus the organization is saying it isn’t a third party, just a coalition of the two existing parties, though its candidate would be a third option.)