I've seen some servers where you have to sign up to their website to become a member in-game and I was wondering what the plugin is? If you do know please tell me ASAP! Thanks.
It's enjin. user panel tags and stuff, you fix the tag options so if it was changed in the website it would sinc the player to the game
I believe this can be achieved through Enjin (as others in this thread have already said). Visit: http://www.enjin.com/minecraft-websites