The site is open to use and participation by anyone as far as posing questions. Anarchists of any stripe except National Anarchists (aka Nazis) and anarcho-capitalists (aka capitalists) are invited to offer answers.
Your observation of the general tendency of most of the regular participants isn't off base, we trend green, post-left, and/or nihilist, but if you look you will find strains of insurrecto-, anarchafeminism, and even sometimes anarcho-communists and syndicalists. We even had a transhumanist participating for a bit a couple years back. There is definitely a -without adjectives strain that runs through some folks thinking.
Due to the nature of the answer/comment format, and the willingness of regular posters to ask probing/critical questions, a lot of those folks seem to dip after not very long, but personally I think they tend to make the conversation richer, even though mostly I think the conclusions they reach and the methodology they use to reach them are wrong.
Personally I am a post-lefty type who would welcome more contributions from other corners of the big tent.