Glowstone
Glowstone is a lightweight, from scratch, open source Minecraft server written in Java that supports plugins written for the Spigot (and Bukkit) API. The main goals of the project are to provide a lightweight implementation of the Spigot API and Minecraft server where exact vanilla functionality is not needed or higher performance is desired than the official software can deliver. Glowstone makes use of a thread-per-world model and performs synchronization only when necessitated by the Spigot API.
