Package Types - Windower/packages GitHub Wiki
Windower 5 supports several types of user-developed Lua modules, or packages.
Addons
Addon packages are much like addons in Windower 4. They contain actual user-facing functionality such as adding new commands, modifying or injecting packets, displaying information on-screen, and so on. They are what most addon developers will be interested in, since, well, they develop them.
Libraries
Library packages are again, much like the library modules in Windower 4. They contain code that may be used by multiple addons. As such, their code is generalized and helps addon developers avoid reimplementing common code fragments.
Services
Services are a special kind of package - unlike addons, they are not loaded on demand, but at program start and they keep running throughout. Services are designed to be small and do only trivial work such as data gathering, with a high degree of availability in mind. They share data and trigger events among libraries and addons.