I am one, so I can shed some light. It’s a tactic more than a philosophy, much like democratic socialism, but in this case arguing that armed unions directly seizing the means of production and serving as a unifier for the working class and training ground for solidarity is the best means to move towards a stateless, classless, and leaderless (or leaderful) society. Philosophy wise we attract everyone from marxists to mutualists (I lean that way).

There’s one major an-synd organization still around, the IWW, a radical union notable for influencing basically every radical, it’s absolutely rock stars of founders and members such as Lucy Parsons (born a slave, married a white man who died for Haymarket, proceeded to call for the homeless to kill the wealthy for decades) and James Connolly (martyred in the Easter rising), and for it being the only group willing to unionize everyone from dock workers to dick workers to freelancers to prisoners.