There is a lot of information available on the project yet, but they tie in with Heroku and AppHarbor. I did find an entry on Bloor Research that has a section talking about JustOneDB.
Here's a small section out of their technical data sheet. It looks like they are using a very different storage architecture that may be very compelling. One of the very interesting things their back end apparently provides is fully indexed query performance with actually requiring indexes. Cool. It look like this is a commercial product. Too bad, it would be fun to take a look at how they are doing all of their cool things :)
JustOneDB uses a unique storage model which is neither row nor column based; but instead stores data by relationship. Data is duplicated and compressed along each relationship such that every query encounters data arranged in optimal spatial locality for a given query. This allows JustOneDB to fully exploit the virtuous characteristics of modern hardware such as CPU cache pre-fetch, bulk transfer rates and multiple core architectures to achieve stellar performance on a modest hardware footprint.