It's actually just a simple table with a couple of additions. (free)
HTMLCAL is a Web calendar maker and editor that lets you maintain a group calendar for your Web site or intranet.
This software will let you maintain live calendars on your site that anyone can view or update from any Web browser. ($25)
HTML Calendar Maker Pro was designed with ease of use in mind. Now you can type your events quickly and easily and they will be transformed into a customized and professional monthly calendar within seconds. Simply follow the on-screen tutorial to create your calendar and then place the finished web page on your site. It's perfect for planning for the weeks ahead or noting past historic events. ($26.50 +)