What are the largest anarchist organisations internationally by membership? I am curious about the relative popularity of different anarchist ideologies, to understand if say, anarcho-capitalism is more or less popular worldwide than anarcho-syndicalism, or something else.
This heavily depends on how you qualify "movement" and how you measure popularity.
The most active revolutionary Anarchists worldwide are:
Anarchism was also saw increased popularity in Greece after EU crisis, however there are no clear organizations with mass support that I can point to.