Very nice port (and wiki). And the package does compile and install okay on Mac using the Carbon widgetset. I didn't try out the example in the wiki, but I did drop some of the controls on a form and they look fine. In the past, it was almost a given that a ported package that had not been tested on Mac would not even get that far. Probably a testament to the maturity of the LCL that such a chronic problem is much less common.
Here are two areas of possible enhancement, both connected to the kind of "antique" nature of some of TurboPower's stuff (and not to your efforts, which clearly have been considerable).
(1) I would guess that it would be unlikely that anyone would want to use a standalone calendar app these days, whereas 10 years ago that might have made sense. For example, on my Mac, schedule events that come in, via e-mail, automatically go into the computer's calendar and these events are automatically synced to my other devices.
However, there might be applications where it would be useful to pull some of this information out of the local system calendar's store and display it in Planit controls. That should be possible to do on any calendar platform, whether Apple or Google or whatever (although probably not in a cross-platform way). I would guess that's where something like the TVpFlexDatastore would come in handy (TurboPower was famous for their tools always having hooks like this for pulling data from anywhere, for example the Orpheus table's GetCellData events).
(2) Since these controls and the available data sources are so general, it seems like they could be used for any application that needs to collect and display "event" type data. For example, data collection for field research, particularly if the collected data needs additional analysis or processing, which would be part of the app.
-Phil