Here's a simple program I have compiled for OpenBSD/Zaurus users: (This program is not yet in the OpenBSD ports collection)

Biorhythm-1.1.2

QUOTE
This program calculates a simple biorhythm plot based on the given date
of birth. The plot starts at the given first day of plot, and includes
the number of days indicated on the command line.

Dates must be entered according to ISO date format, that is:
YYYY-MM-DD, four digit year, two digit month, and two digit day of
month.

The default plot includes emotional, intellectual and physical
curves. This may be overridden by command line options.

To install just un-tar.gz and read the included HOWTOINSTALL text.

The original source code can be found here: http://shh.thathost.com/pub-unix/#biorythm

Further information concerning biorhythms can be found here: What are Biorhythms?