The most modern and support friendly public SpigotAPI
This SpigotAPI supports and enchances how implement KnockbackAPI support from different spigot forks, along with helping the issue of EntityHider with spigots that don't have it.
To contribute or add another spigot, just create a new module with the same package path, then implement the correct API interface and add the usage from the Spigot. Besure to never push the actual spigot jar here, only its API with permission of developer. You can then create a pull-request with your changes. This API will be used in a lot of RefineDevelopment's plugins.