There comes a time in every alternative OS user's life when they decide they'd actually like to use a program that typically runs on Microsoft Windows. Typically, on Linux, it's around day one. It happens less often (in my experience) as a Mac user, but eventually some tantalizing gaming experience or obscure utility will call across the void, and there's no way your 128GB SSD has enough room for a Boot Camp copy of Windows.
And that's when Wine pops into memory: the 23-year project to run Windows applications on Linux, Mac, and other Unix-like operating systems. In my experience, it almost never works, but it often almost works, which is still impressive. "Wine," which stands for "Wine Is Not an Emulator," acts as a substitute for Windows. Where an application expects Windows to provide or service or resource, or respond to commands, Wine steps in and attempts to do the job. It's a quixotic effort, both because Windows is so large and complicated, and because it's a moving target.
Now Wine 2.0 is out, which is a huge milestone for the project. It has more support for more software, includes a lot of graphics speedups, and even supports retina displays on Mac. The list of compatible software is indeed impressive — the latest and greatest apps are rarely supported, but many relatively recent "classics" like Left 4 Dead, Fallout 3, and Office 2013 are supposedly operational.
The last time I tried to use Wine was to play Path of Exile on my MacBook Air, which barely worked. I ended up buying an external hard drive and putting Windows on that. More recently, I just have a Windows desktop for when the gaming itch hits me. But the next time I'm stuck in an alternate OS wasteland, I'll probably give Wine another shot. Maybe it will all work out this time.