(Google Play Link)
We actually built this one a while ago, specifically as a response to this Reddit post. Implementation took a bit of work but was relatively straightforward. We were surprised to learn that all the actual sphere mapping/positioning information was stored as metadata inside the JPG, and that you were expected to use a bunch of Adobe custom libraries to read that data. That took a day or so. Once we had the data, we needed to create an appropriate sphere model with reasonable mapping, and write a shader that properly offsets everything using those instructions. That went fairly quick, though getting the camera to behave well while respecting the bounds of the image took a few tries. All told we had a largely working project within a couple days.
The real problem is, I wanted to include some default images. If nothing else, I needed one for the Play listing. I make a point of staying legal for things like that, and normally I'd either ask an artist to make something, or maybe browse some stock photo sites and look for good images we could get rights to... but we can't really do that here, as it's a fairly new feature and you can't find them on the usual photo sites. The nature of the image makes painting one rather non-trivial, too.
So, I started contacting folks who had good ones (mostly on Google+) asking for permission to use their images, and mostly got ignored -- I'd imagine I sounded like a scammer or something. Eventually I came across an excellent beach image by Kevin Flannery and he kindly granted permission to include his photosphere in with the product. It's just one, but it's enough to make the market listing and have something sane looking when you first run the product.
After a bunch of delay as we finished off other projects, I finally sat down on Sunday and got Photosphere up and available for download. Amazingly, even before I wrote this, AndroidPolice had already noticed and written an article about it. Can't complain about that. :)
This is currently a relatively lean product, so we've got a fully-functional free version up. As Photosphere support gets bigger ideally we can hook in some additional functionality and have a paid version as well. We'd love to have Picasa integrated, for example, once they have a way to filter to Photosphere images. For now though it works, should handle any photosphere on any device, and I hope everyone enjoys!