Enclosed SMP is a survival server with a map that is only 1500 blocks wide. That means everyone is packed close together and it makes survival feel way more intense.
The goal is to survive and try to become the richest player on the server. Since space is limited you will run into people a lot and it can get competitive.
The server has a small friendly community and some helpful commands like sethome. It also has an economy with auctions so players can buy and sell stuff.
Moderation is active so hacking is not an option. It is also meant to be lag free and it has zero pay to win.