This is a service offered free to people who have Nokia accounts who sign up a developer account (which is also free.)
It's purpose is to let developers use a Windows Phone that might not have access to one. It allows you to deploy xaps directly to the phone and offers a number Nokia devices. Not all of them are Windows Phones, and some are in other languages besides English. Some of the Windows Phone devices have SIMs in them and some of them actually have phone numbers where you can call it. A new feature that's available is the onboard cameras have been enabled on the Lumia 820, 920, 925 and the 1020. I'll take screenshots when I can.
The Phone is sideways for photos, so here's the screenshot of the about page.
Also, some of the Windows Phones have a manually installed OEM dev app, On-Device Diagnostics Tool.
RDA for Lumias
RDA's Twitter News Account for new features and Devices
NOTE: I've noticed with the 928, the device lags really behind. SO FAR BEHIND, the frames you might be seeing are from minutes ago.
EDIT 1: Simply exiting the program and starting it up again possibly remedies the video lag issue. Doesn't always work, but it worked well enough to make a video finally.
EDIT 2: There isn't much info about on the ODDT from Nokia. I've uploaded and embedded the videos demonstrating the oem diagnostic tool and some other stuff I did in the session.
Sorry about the first video. Its mostly in monochrome due to the settings I had at the start of the video. After some time into the diagnostics portion I had bumped the quality to 3 or so where it displays color and animation at a decent rate.