I noticed that the last mod was done in 2008. 
Do you think we will ever have a Calendar working on the mac platform?
Frankly speaking, i think we'll get native mac calendar with Cocoa widgetset finished.
Cocoa widgetset development is currently freezed (waiting for some FPC updates)
I want to create lots of programs which I would love to have working on a mac as well as the humble pc.
You can make a platform independent Calendar, based on LCL components (i.e. TStringGrid), rather than system-native calendar widget.
Btw, if your calendar is good, it might be become part of LCL, as a replacement for missing Carbon native-calendar.
Patches are always welcomed.

Let's help each other.