I did a quick evaluation of Reaper v3.74 for the Mac, and it looks very nice!

I had a tiny bit of trouble with the user interface and some of the Preferences for while, but doing a bit of reading and a few experiments resolved everything . . .
Part of the problem was the result of Reaper tending to prefer to display numerical values with basic formatting, which took me a while to realize, where for example in the "Audio Device" configuration pane there is a variable named "Request sample rate" with the default value "48000", which looked a bit strange until I realized that it was "48 kHz" or "48-kHz" the way I am accustomed to seeing it formatted . . .
Reaper will do it automatically, but I was experimenting and had checked the option box for the "Request sample rate", and since the option box was checked, it was very important that the numerical value be correct. . .
So, knowing that the WAVE file I was using to test playback was done at standard CD resolution (44.1-kHz), I changed the value to "44100", and the playback switched from being choppy to being very smooth . . .
There are times when it is useful to be able to delve into numerical values for doing a bit of fine-tuning, so this is fine with me, and it did not take very long to discover how it works . . .
I need to see how Reaper works with VSTi instruments and VST plug-ins, but it looks good so far, and I did a quick experiment with ReWire where Reaper is controlling Notion 3, and it moves the transport, so there is some level of ReWire support, although I did not do a lot of ReWire testing . . .
Summarizing, the Mac version of Reaper is intriguing, really . . .
Really! 