I have used several well-known calendar and todo list apps that is around and here's what I found relatively better than the other on the PC :
kontact
It's on linux, but this app alone could justify your switch of OS. It's that good. It's a full-fledged PIM but you could just use it's
KOrganizer component as standalone calendaring and todo list, although you'll miss a very nice integration with mails, feeds, notes and contacts apps.
Assuming you can live within it's functional area (linux, kde, device and os it's support for synching) it's the best I know on PC.
Some highlights/impression :
* Nicely looking : don't refer to much on the outdatred-screenshot on the site, the current state looks much better
* Simple, unbloated (at least from geek-standard of bloatedness
)
* the thin red line of current time on the calendar view is a simple yet elegant and useful touch, adding a "realtime-feel" to it
* high standard compliance (vCard, iCal, vCal, online calendar access, etc..)
* I haven't found any typical use case of calendar/todolist that it does not support yet
* mature and stable with no bugs I have encountered yet in my use of it
* could make hierarchical interrelated tasks
* command line operation for those who into scripting and automating some recurring/boring operation or just want to do typical action which not need to fire up the whole calendar