The Binding of Isaac: Unholy Edition is a DRM-free PC and Mac version that includes a free Steam gift key, the full soundtrack, a poster and a 40-page art book. Developed by Edmund McMillen of Super Meat Boy's Team Meat, The Binding of Isaac premiered on Steam in September along with an adorable plush from the Team Meat Shop on Etsy.
If you don't yet know why that darling doll is crying, go ahead and pick up The Binding of Isaac on Steam for $5, or wait for the Unholy Edition to launch in Europe at an unknown price. Or you can just listen to this song, whose recurring line is "To the basement, people, to the basement / Many surprises await you / In the basement, people, in the basement / You hid there last time, you know we're gonna find you."
Update: Merge Games, the publisher behind Isaac's Unholy Edition, is based in the UK. While it doesn't list the retail version specifically as UK-only, we assume that is, in fact, the case. All you North Americans can just crawl back into your basements now, thanks. We've reached out to Merge Games for clarification.
Update 2: Merge Games has confirmed The Binding of Isaac's retail launch for the following regions: UK, Ireland, the Nordic countries, the Benelux, Italy, the Czech Republic, Greece, Turkey and South Africa. Merge Games also handles publishing in Australia and New Zealand.