Jewish Calendar calculates dates, holidays, parshiot, and more. It can handle both diaspora and Israeli schedules. And it works natively on both Mac OS 9 and X.
A guy named Frank Yellin wrote this. I have officially adopted it, carbonized it, and we'll see what happens now.
Version 2.1.2 (16 April 2002)
Remembers menu settings (Diaspora/Israel, Gregorian/Julian, etc.) and page setup
Uses sheets for printing UI
Version 2.1.1 (27 December 2001)
Small arrows in year picker dialog now work properly under Mac OS X
New icon (thanks to Jomy Muttathil)
Adjustment to Yom HaShoah date calculation (thanks to Ben Stitz)
Minor tweaks here and there
Version 2.1 (24 September 2000)
Carbonized it (fizzzzzzzzzz....)
Jewish Calendar is currently available for download as a ZIP archive. If you have Mac OS 10.4 Tiger, you can open it; if you have Mac OS 10.3 or earlier, go to the Aladdin Systems web site for an extractor. (If you're running MacOS 9 or 8.6, get the StuffIt compressed version, and if you're running 8.6, you'll need CarbonLib 1.3 or later which is available from Apple.)
Download Jewish Calendar 2.1.2 (26K) from Pittsburgh.
If you have a 68K-based Mac, or are running a system earlier than 8.6, you can run Frank Yellin's original version:
Download Jewish Calendar 2.0 (20K) from Pittsburgh.