The "calendar(1)" program is not a part of Red Hat Linux Enterprise 3.
Many long-term Unix users expect to find this program and use it to
send themselves e-mail reminders of appointments.  This program works
whether or not they are logged in.  It uses a plain text file for
data.  This program is a part of traditional Unix operating systems up
to and including FreeBSD.

This program is better in many respects than the GUI-based calendar
and personal information manager programs in that it works whether or
not a user is logged in, it works on a text-only login session and its
output is via e-mail.

Our users often travel to remote sites and forward their mail to the
remote site.  When they use "calendar(1)" they do not have to depend
on a Linux environment at the remote site, an MS Windows environment
at the remote site, etc.  They can view their appointments in a daily
e-mail message and use an ssh session back to their home account to
update their schedule.

It ain't pretty but it's portable.