It's an odd term which has come out in the last year. Most folks, if you ask them what an alt-right means....will probably suggest some type of new technology or some mental disease.
The news media has coined 'alt-right' to mean a 'loose group' (hint: they aren't in the Klan, a 4-H Club, or a registered lobby group). This group, according to the news media, is OUTSIDE of mainstream conservationism. This usually means that they aren't real conservatives or moderate conservatives or flexible conservatives. I know....this is the news media who is telling you this, and you have to wonder where they got their definition, but they would just grin if you asked.
The news media will then tell you that these anonymous people (always faceless for some reason....maybe hoping to trigger you to identify them as Klan folks)....use Twitter, Facebook, social media, YouTube, and Breitbart/Drudge to get their message out. If they were legit, they'd be using the news media (don't you realize that).
Their goal (the alt-right) is to challenge social "norms". Those norms are never explained in detail by the news media through. One has to accept that there was a norm last year, or in the last decade, and that the evil alt-right are trying to replace that norm. How many norms exist? Unknown.....but it must be into the thousands. Will norms just always stay the same? Well....if you asked the news media....they'd just grin because no norm EVER stays the same....well before the alt-right ever showed up.
Is there a alt-left? Officially, via Wiki? No.
In reality, an alt-left has been around since the 1960s and is simply a fixture of the news media, lobbyists, political parties (both Republican and Democrat), and even religious fixtures. All the alt-right guys did was figure out the gimmick and build a modern media device to deliver the message. Social media, YouTube, and the Internet actually gave them a platform. The amusing thing is that the alt-left thought they owned the platform, and now.....they have to share it, and actually get smart on the competition.
This fight between the alt-right and alt-left to legitimize racism? Oddly, both seek to ID the other as the racist in the room. If you measured the usage of the term "Hitler" over the past year within the social media or news media.....the term has likely be used a billion times. On the humorous side, you can ask most 16 year old kids today, and half of them have no idea who this Hitler guy is but his name sure gets mentioned an awful lot.
Eventually, I think some smart guy will invent a new group called the alt-alt-right or the alt-alt-left, and freak out the social and news media crowd. A bunch of PhD guys will assemble in Princeton and try to work out some definition for Wiki over some weekend, and admit that they've never really heard of such a group before, but it must have something to do with Hitler.