Goblin SMP is a vanilla survival server that tries to make players actually meet each other. The map is kept tighter so bases matter more and you do not feel like everyone is a million blocks away.
The world border starts at 200000 by 200000 and it expands every month. That means new land opens up over time and the world keeps changing as people spread out.
It is pure survival so you can build trade explore or fight. The rules are pretty simple too. No hacked clients like x ray or esp. No exploits and no lag machines. Respect the server and other players.