Bukkit topic
Bukkit is a Minecraft server modification software and API, and while the original project itself is stale, forks like PaperMC and Spigot are actively maintained, and most plugins and servers use some variant of Bukkit.
advanced-region-market
A Bukkit/Spigot plugin for renting/selling WorldGuard regions
black
an object-oriented inventory framework for spigot
Auto-Tune
Automatic Minecraft Economy Plugin
Bukkript
Bukkript is a custom Kotlin Scripting Definition for customizing Minecraft Bukkit servers
KotlinBukkitAPI
KotlinBukkitAPI is an API for Bukkit/SpigotAPI using the cool and nifty features Kotlin has to make your life more easier.
Geyser
A bridge/proxy allowing you to connect to Minecraft: Java Edition servers with Minecraft: Bedrock Edition.
Floodgate
Hybrid mode plugin to allow for connections from Geyser to join online mode servers.
MinecraftDev
Plugin for IntelliJ IDEA that gives special support for Minecraft modding projects.
Mirai
Mirai 未来 - A powerful Minecraft Server Software coming from the future