For some, yes. For others, like CraftBukkit and Hamachi, nope. It's free.
Actually, no.
I guess you are talking about minecraft...since there is not technically a thing like a "freebuild" server, yeah it does...youll need craftbukkit, i think mysql and php.
it's a plugin called Permissions.
You will need a CraftBukkit server (see link below) with a compatible build to install the plugin.
This is the type of CraftBukkit server that runs an RPG Plugin that allows leveling up, in-depth combat techniques, etc.
There are tons of tutorials out there. If you are running Minecraft Beta 1.8, you should update to the newest version.
If you have a normal server, you have to op people from the console to give them permissions. If you have a craftbukkit server, you can download a plugin for permissions.
Download the latest CraftBukkit server from bukkit.org(top-right corner of the home page). For plugins, click on 'Get Plugins'.
In order to do this, you should make your server run on CraftBukkit (Download the latest recommended build [DO THIS AT YOUR OWN RISK]) and download a plugin for this kind of labeling.
Unless you have a plugin for a CraftBukkit server (although I don't think there even is a plugin for this), then you can't. Just don't give your IP out to people you don't want joining your server.
This is the modified servers list for Minecraft Servers. The use of Bukkit / Craftbukkit will enhance the server with a lot of great features, to help give the server more options/functions and it gives an gateway for plugin designers to make even more crazy functionality to the game.