rcade Bukkit is GPL, derivate work from GPL need to be GPL and their source open (http://www.gnu.org/licenses/gpl-faq.html#OOPLang). CraftBukkit cannot be GPL or LGPL, it contains Minecraft code, to be valid it'd need to have Minecraft code open source. CraftBukkit was taken down, not Bukkit. There's no way out, either they remove bukkit from craftbukkit (impossible) or the minecraft server jar becomes open source. P.S. Also all plugins built for Bukkit are supposed to be GPL.