Flat Calendar is a simple calendar system. Flat Calendar was last updated in 2002 and is no longer supported by the author.
From the Author
Flat Calendar was designed for those of us who need calendar and event book functionality but do not have access to a database, or would simply prefer to store the data in a flat text file. Unlike most of the calendar and event book scripts available, Flat Calendar stores all its events in files on the server without any use of a database.
Authors website: http://www.circulargenius.com/flatcalendar