A new event system for plugins to register handlers for specific events that relate to the startup or reload of servers.
We already have an event system, why do we need another one? Fair question. The answer is in the lifecycle part of the name. Some of these events fire well before JavaPlugin instances are created, before the MinecraftServer instance is created, right at the very start of server startup, even before all the registries have been initialized which is like the 2nd thing to happen on a vanilla server. The existing Bukkit event system is not designed to exist at this time, and modifying it to support this environment is more trouble than just having a separate system for specific events that can fire during this early initialization.