I was chatting with some people on Vent the other night when it came up with one guy was having a problem: both SimulationCraft and Rawr (fine tools in their own right, don't get me wrong!) seemed to be low-balling his death knight's DPS - by at least 1000 dps in some cases! So when I mentioned Kahorie's DK Simulator, I was a little surprised when I was met with first dead air, then "huh? What's that?"
Well, I smell a post. Let's get started with a quick tour of Kahorie's fine, fine tool!
Caveat: I use Windows. I am not a Mac person anymore, though not by choice. Anyway - these instructions should work fine on a Mac if you use BootCamp or some sort of tool that lets you use Windows apps on OS X - Parallels and VMware Fusion both being popular choices. It's not a terribly complex app, and if you can run .NET apps, you can run this sim.
First things first, you need to download the simulator. On the downloads tab, you'll see a big list of downloads - but the only one you need to worry about is the very first one, Kahorie's DK Simulator.zip, because it always points to the newest version. Unzip it, and place the folder inside somewhere convenient - your desktop, a downloads folder. There's no installer to run - open up this folder, and look for this icon, then double-click it. Kahorie's DK Simulator runs right out of the box. (Yours probably won't have a little green checkmark on it - mine does, because I keep my simulator stored in my Dropbox, which is a whole 'nother story altogether.)