The Mac port demo is now on Steam for some early testing at
http://store.steampowered.com/app/270150Despite the odd wording, "Download PC Demo" should also work for Macs Follow the Download Mac Demo button on the right hand side to begin download & installation.
Feel free to drop me a line on this thread how the demo is behaving in your system.
I've personally tried it with Mac OSX Mavericks 10.9.5 on Mac mini (late 2012) with Intel HD4000, 720p fullscreen, no antialias, yes shadows and post processing, seems to be running a steady 30fps (can be checked by adding
debugmode in launch options and pressing F9 in-game (I know, I know, should've made that more straightforward by now

)). In fact, it's so steady I'm thinking it's being clamped by something, and it seemed to happen regardless of vsync on/off. Needs more investigation. Keyboard and mouse felt pretty much normal to me.
Another system it has been tried was Mac OSX Yosemite 10.10.1 on Mac mini (late 2009), the tester fellow said the framerates were pretty poor, but turning down postprocessing helped significantly. I was told there was some noticeable input lag with keyboard controls.
A known issue is with the Configure tool not receiving focus when it's starting, but you can see it start on the dock, just click on the icon to make it pop up.