BukkitOpFix - a Spigot plug-in that re-implements permission levels for OPs which were always broken in Bukkit.
You can set the OP permission levels using the "op-permission-level" configuration node in your server.properties file.
To read more about it in the (now seems to be outdated) MinecraftPedia, follow this link: http://minecraft.gamepedia.com/Server.properties