Surface Duo is a new Android-based smartphone that was developed with the cooperation of Google on the software side. The device doesn't appear to be running any recognizable flavor of Android, and is likely using Microsoft's own take on the world's most popular operating system.
The device itself looks like a shrunken down version of the Surface Neo thanks to its dual-display design. Each display measures 5.6 inches across, and when unfolded gives you the screen real estate of an 8.3-inch (diagonal) tablet. Like the Surface Neo, the Surface Duo features a 360-degree hinge, but this smaller device is actually pocketable -- as it should be -- since it is also a smartphone. You can run two apps at a time (one for each display), or you can expand one app to cover both displays.
Powering the Surface Duo is a Qualcomm Snapdragon 855 SoC, and according to Wired, it's currently running a heavily tweaked version of Android 9. However, Microsoft says that the Surface Neo won't even ship until Holiday 2020 (to give app developers a chance to catch up), so it's highly likely that the SoC and operating system will be upgraded by then (perhaps Snapdragon 865 and Android 10 or Android 11).
At this point, the Surface Neo is an interesting development in the fast-changing smartphone space. Samsung introduced us to the concept of foldable displays with the Galaxy Fold, but that device was plagued early with design issues (which may or may not have been completely resolved with the refreshed model). The Surface Neo is going after the same basic of idea of a pocketable device that fit in your pocket, but unfolds to give you more screen real estate.
Both have their compromises though. The Galaxy Fold's display is uninterrupted, but you do have to deal with a still visible crease in the middle of the display and the fact that it is constructed of plastic that can be scratched easily. The Surface Neo has much more durable Gorilla Glass displays, but you have to contend with the hinge which can get in the way of the "immersion" factor when viewing content full screen.
With that being said, it's nice to see Microsoft firing on all cylinders when it comes to innovation and we look forward to see what the next year will bring in refinements to the design before it is ready for public consumption.