Nautilus is a core mod which modifies the base game to add hooks and features for other mods to take advantage of. These modifications are done to the base game using the Mixin framework.
API Features
Items can control their enchantment glow color. An example of this can be found here.
Events
ItemDeathEvent - This event is fired when an EntityItem would be destroyed from damage. This event can be canceled, which will prevent the item from being destroyed. Example.