It's true that the standard Windows calendar control hasn't changed much over the years, but I thought you were trying to go back to the retro/modern minimal style?
I'm somewhat reluctant to try to find another control, partly because the existing one is part of the standard, and at least theoretically adjusts to the changing overall Window style / theme. There are other variations out there, but typically are part of some suite based on .Net or part of a web framework, making them difficult to integrate on their own, and probably subject to style disconnects as Windows evolves.
And if you really want flexibility, you could roll your own (although it would take a lot of work because there are so many individual parts to it, and partly because there's a lot of interactive functionality built in to the control).
There are a couple of attributes (mainly colors) that we could enable via CTLOP_CHG operations (see
Calender control operations). For example setting the background color of the title...