Quick background: For the first time ever I joined a large guild, 75+ members on at a time, 800 total. I got vary frustrated with keeping track of everyones information so I have been writing addons to do it for me. I wanted to put the information in the GuildMemberInfo frame however there is no easy way to do it so i wrote my first lib.
It is designed to be a quick framework to add information about people in your guild to the GuildMemberInfo Frame. More information about how to use the framework is on the WoWAce page.
This is my first framework so I am looking for ideas on how to improve the addon. Right now the only major piece that I think is missing is a way to un-register your module(s).
If your project actually has a GUI and does something visible/accessible to the end user, it is an addon, not a library. A library would be a project that only provides functionality for other addons to use.