Iptables duplicate work for each family and is using a socket protocol which is far too static. Xtables2 is an ongoing effort to evolve the packet filter. It aims at providing finer frained modification (and not the whole ruleset modification).
- rule packing: increase cache hit.
- family independent: no more IPv4 and IPv6 specific code. Only the hook remains specific as they are dependant of core network.
- xt extension support
- atomic replace support
xtables syntax is quite similar but not the same. libxtadm is a high-level library for ruleset inspection/manipulation.
More info: xtables.de