Bukkit

A powerful yet simple way to manage towns.

A plugin to bring 4chan/Yotsuba-style greentext to your Bukkit SMP server.

Announce fails and wins via command, for all the server to see.

A simple plugin to let a player logging in to an empty server know they are not as alone as it may seem.

Make sure everyone knows if they use a word that GNU thinks they should avoid.

A lightweight way to filter your server's chat.

A server plugin and desktop client pair to help you admin your server even when not logged in.

YAEP (pronounced "yep!") is a lightweight alternative to heavier "essential command" plugins like Essentials.