This is a very simple plugin to workaround lag that can be caused by zombies in 1.6.4.
Simply put, when zombies are trying to target something but can't get to it (and with the new horde feature, that happens a lot), they will try to recalculate a route on every server tick. Pathfinding is expensive, so even a few zombies doing this can lag out a server. This plugin works around this bug with two features.
Firstly, it can kill all zombies that aren't despawn-immune, and are more than a certain distance away from players (by default, 20, though you can specify any distance, including 0)
What are despawn-immune zombies? Any zombies that wouldn't despawn naturally, because they have a name tag, or they've picked up items etc.
Secondly, it can list all the despawn-immune zombies currently active, so an admin can teleport to them and decide if they need to be killed. This is not automatic because the decision will vary from server to server. Chances are, any zombie with a name is someone's "pet". Chances are, a zombie carrying tons of stuff has picked that up off a player's corpse and he's coming back to slay it and pick it up. But chances are, a zombie deep underground carrying a slimeball is safe to kill.
There is one permission node required for using the command - zombiekill.zombiekill (defaults to op-only)
This plugin works fine on 1.7 servers. However, the bug this plugin is designed to solve has been fixed in 1.7, so there may not be a lot of point to it ;)
