You'll get to download a preview edition of Visual Studio for Mac sometime during Microsoft's Connect() conference, which kicks off November 16th. It's not certain when you'll see a finished version, but the timing of the preview likely puts the polished release sometime in 2017.

The Mac version may seem odd at first blush. Wouldn't this discourage developers from writing on or for Windows? However, it's more logical in the context of Microsoft's "mobile first, cloud first" strategy. If you're already building apps on a Mac, you might as well build them in a tool that makes porting to Windows easier -- and Microsoft would rather you write for its cloud platform on a Mac than risk losing you to a rival offering. The Redmond crew no longer benefits greatly from making you buy a Windows PC to write code, and the new Visual Studio reflects that reality.

Update: As promised, the Visual Studio preview is available to download.