In the Mac universe, there are several:

  - Eastgate's Tinderbox
  - Zengobi's Curio
  - Momenta's Agenda
  - I think Bear app does this too.

In the case of Eastgate, a subscription is about $90/year, and well worth supporting a great tool and cool developer.

As I've said, I'll happily spend money for good tools, but I want to use said tools if my subscription expires.