Sadly there isn't much of a choice :|
You have
Necronia as Shiva mentioned, but you need a beta key (14$, out of stock I think) and there isn't much to do in beta until Conqueria (mainland) is available.
Website-
http://necronia.com/
0-5 people? due to Conqueria not being released yet.
TheOTServer seems to have some pretty custom vocations. I didn't played it much though due to it being a teleport server, and once you get to a certain level you're forced to PVP in order to level.
Website-
http://theotserver.com/
0-5 people? Never really seem many people on :/
Tibia kingdoms is a pretty nice one. The owner is pretty dedicated to working on it. Has 12 custom vocations which is awesome. I had some fun playing it a while ago, not sure how it is now.
I'm sure a lot more was added, and or changed.
Website-
http://www.tibiakingdoms.com/
10-25 people
Deathzot is the last one lol. It has all custom vocations which makes it interesting. I didn't bother playing it though cause it's a straight up bot server and I don't have a bot, nor use one. If you decided to play on there know before hand you will need to bot, even multiple accounts like a lot of people do.
Website-
http://deathzot.net/
Usually like 220~people, give or take. (most are botters, and some have multiple accounts/characters)