An API that adds several client and server side functions, both for developers and those who make resource packs, among them:

• UI Definitions, to add or modify countless elements of the screens and GUI, either using resource packs (main function) or by code
• Essential Events, most of them abstracting directly from the mod loaders
• A Common Network, to send and register payloads in a unified way, requiring almost zero changes between the supported versions
• Several common implementations among modloaders of item, fluid and energy storage with the correct exposure for the respective APIs
• A way to have block lighting levels with access to Level (only implemented in Fabric, Forge and NeoForge already have this)