Dissent claims to be able to be resistant to Sybil attacks.
Dissent seeks to offer accountable anonymity, giving users strong guarantees of anonymity while also protecting online groups or forums from anonymous abuse such as spam, Sybil attacks, and sockpuppetry. Unlike other systems, Dissent can guarantee that each user of an online forum gets exactly one bandwidth share, one vote, or one pseudonym, which other users can block in the event of misbehavior.
However, I went through 3 of their presentations and the only 'accountable' anonymity it promises is to successfully blame a bad actor in a dining cryptography network (DC-Net). There was no mention of how to prevent multiple identities from the same user. I could imaging anyone could connect to the Dissent network through TOR and disguise their multiple identities, merely acting as different people and following the rules.