DataStore_Agenda is part World of Warcraft Add-on that is part of the DataStore series. It is compatible with all versions of the game.
Its purpose is to scan and store data related to Calendar, Raid ids, Friend List (and later to-do-lists, personal notes, and maybe more) for all your characters, and act as a data abstraction layer for client addons, which no longer have to scan or store this information.
More information can be found on the main page : DataStore