I’m running AnyRail (a Windows app) on Windows 8.1 within a VirtualBox virtual machine hosted on my 2012 MacBook Pro which is running Yosemite 10.10.3. It is rock solid and more than fast enough.
Only within the past week, I noticed that Atlas also has Track Planning Software which includes a 3D mode to better visualize the height, clearances, and scenery of your layout. I have not had a chance to try it yet. But it does run on Windows 8.1 within the same VirtualBox on my MacBook.