I just uploaded a simple calendar widget that appears in Notification Centre of your Yosemite-powered Mac. It doesn’t connect to the system-wide Calendar, instead it just displays a simple month view.
It’s currently source-only — so you need to be a developers or at least comfortable with Xcode — but is pretty much feature complete.
As is often the way when you write software for a living, I found a problem and I felt the need to fix it. As with most of these problems, it took longer than I anticipated but I’m quite happy with the result.