I've only worn this dress once after I got it from Urban Outfitters. It's called the Rapscallion dress by Samantha Pleet. It has detachable straps so you can wear it like a halter, with both straps, or without them.
The original price was $63. I'm selling it for $35.

Here's a website that shows some pictures with a model wearing it. It looks better on a someone with more curves, in my opinion:
http://www.hipsterchic.com/rapscallion-by-samantha-pleet-romper/