browsing repositories can be fun! i just found this gem in ubuntu's repos while looking for a calendar app:
mencal
A menstruation calendar
Mencal is a menstruation calendar written in Perl.
It is a simple variation of the well-known Unix command cal. The main
difference is that you can have some periodically repeating days highlighted
in color. This can be used to track menstruation (or other) cycles
conveniently.
Author: C. McCohy <mccohy@kyberdigi.cz>
Homepage:
http://mencal.kyberdigi.cz/english.html