libivykis is a thin wrapper over various OS'es implementation of I/O readiness notification facilities (such as poll(2), kqueue(2)) and is mainly intended for writing portable high-performance network servers.
Snort2c attempts to be a improved version of snort2pf wrote by Stephan Schmieder with some advantages: kqueue, pf table support, pf ioctl's calls and others. It works monitoring snort's alertfile and blocking attackers ip using pf calls.