Bukkit is described as 'Free, open-source, software that provides the means to extend the popular Minecraft multiplayer server' and is a minecraft server in the gaming software category. There are six alternatives to Bukkit for a variety of platforms, including Mac, Windows, Linux, Minecraft Server and Minecraft apps. The best Bukkit alternative is Glowstone, which is both free and Open Source. Other great apps like Bukkit are PaperMC, LeafMC, Spigot and Cuberite.
Glowstone is a lightweight, from scratch, open source Minecraft server written in Java that supports plugins written for the Spigot (and Bukkit) API.
Glowstone is the most popular Windows, Mac & Linux alternative to Bukkit.
Glowstone is the most popular Open Source & free alternative to Bukkit.
Paper is a fork of the Spigot server implementation (which is itself a fork of CraftBukkit). Paper strives to bring improved performance, more features, and more APIs for developers to build awesome plugins with.
PaperMC is the most popular Self-Hosted alternative to Bukkit.
Simply put, Spigot is it. Spigot is the most widely-used modded Minecraft server software in the world. It powers many of the top Minecraft server networks around to ensure they can cope with their huge player base and ensure the satisfaction of their players.
A custom Minecraft compatible game server written in C++. It's a fast, lightweight, and awesome replacement for Vanilla.
Cuberite is the most popular Android alternative to Bukkit.
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Good alternative for bukkit. Spigot have bukkit plugin support.