Hope Not Hate (Twitter: hopenothate_USA)
By way of making a dramatic entry, this seems to have been timed to co-ordinate with the announcement of their epic undercover project: Patrik Hermansson, an extremely brave young Swedish grad student, infiltrated the alt-right and lived undercover in the movement in London and the US for nearly a year, wired for sound and carrying hidden cameras. This ultimately included being at Charlottesville and witnessing the car attack that killed Heather Heyer.
The documentary is coming soon, and the comprehensive report on the international alt-right (for which the infiltration was part of the research) is here:
The International Alternative Right
New York Times: Undercover With the Alt-Right
Raw Story: ‘It’s gonna end with concentration camps’: Alt-right executive boasts of a future Europe with Hitler on their money
I love HnH; I've supported them for years and have friends who've volunteered for them. They have a long history working against fascist and far right groups in the UK, through research, infiltration, legal action, anti-racist/xenophobic education and campaigning, and their work seems to have naturally become international as the "alt-right" itself has (e.g. with the "Defend Europe" boat).
So I think their expertise (and the willingness of their reporters to put their necks on the line like this, holy fuck) is going to be a hugely valuable resource for people fighting this shit in the US too.