Download of InterCal 2.2 for Mac was available from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The software is categorized as Productivity Tools. This free software for Mac OS X is an intellectual property of Denis A. Elliott. We recommend checking the downloaded files with any free antivirus.
From the developer:
InterCal is a date conversion program and perpetual calendar. It is not a personal appointment calendar.
The program displays calendars, one month at a time, for any month of any year in any of nine implemented calendar systems. For each day, the corresponding date in any other system can be shown˜thus an entire month is converted at once.
You may want to check out more software for Mac, such as MenuCalendarClock Entourage, Chronos or iCal Reply Checker, which might be similar to InterCal.