Web Based Calendar Software
How to Embed a Google Calendar in Your Website
It only takes a few steps to convert a Google calendar into a widget for your website. This how to shows you how to embed a Google calendar right into your site.
While not a CGI, this script will help you add an event calendar to your Web site.
CoffeeCup Web Calendar
CoffeeCup Web Calendar isn't free, but it allows you to create a Flash calendar for your website. This means that your calendar will only be hosted on your website and you can customize it to match your site's colors and style.
Google calendar provides you with a lot of options for your calendar and once you've got it set up, you can easily embed the calendar in your website. Read a review of Google Calendar from the About.com Guide to Google.
HTML Calendar Maker Pro
Calendars are a great way to build community on your site, and this program makes it easy.
LoCalendar offers free (ad-supported) and paid calendaring options that you can then embed on your website. It has a lot of features and is fairly easy to use.
A highly configurable Web calendar for a reasonable price.