Minecraft/Servers

A Minecraft server allows anyone to create a world that players around the world can connect to.

Vanilla
Original/unmodified server that Mojang distributes, but not commonly used on public servers due to griefing.

Bukkit
A previously very common server that no longer exists due to a DMCA takedown request.

Spigot
As Spigot was based on Bukkit, it was also hit with a DMCA takedown. Spigot has been modified for newer versions of Minecraft, and no longer contains the code that caused the DMCA. It is the most common type of server used.

Forge
Forge allows mods to be added to a server. Everyone who connects usually requires that mod to be installed.

Cauldron
Cauldron was a Forge server that allowed Bukkit plugins to be installed. It was hit with a DMCA takedown and no longer exists.

Sponge
Created in response to the DMCA takedowns of Bukkit, Spigot, and Cauldron, Sponge is a server that works on top of Forge, as it is a mod that is installed onto the Forge server. However, players who connect do not need the Sponge mod nor any mods that work with Sponge.