The Improv is a modular engineering kit that comes with a CPU card and a separate feature card to connect it to. The CPU card powers the device while the feature card provides convenient access to the on-board capabilities of the CPU card through a variety of ports and pins on it.
This unique design allows one to have multiple CPU cards for different projects, upgrade the kit by ordering new CPU cards for additional features or feature cards for different sets of ports and off-board components.
Improv comes pre-installed with the Linux-based Mer operating system. We chose Mer because it has been designed specifically for device development, has a thriving community of both companies and enthusiasts and has a proven open governance model directing development. You aren't locked into this, however: you can install the operating system of your choice.
Improv comes with a Linux distribution based upon the Mer operating system preinstalled. The full image can be found [here http://makeplaylive.com/files/improv-images/plasma-active-armv7hl-sunxi-eoma68-improv-nand-latest.raw.bz2] and can be re-flashed any time on the device.
On this site, there are several ready to use, nand and microsd based images, that are described here. On the same Linux-sunxi wiki page, there is described the procedure on how to generate operating system images based upon Mer and Plasma Active.
It's possible to install any different operating system on the board, or to boot from the microSD card.
On the Linux-sunxi wiki, you can find a tutorial on installing a generic operating system in the nand, from a system running on top of a microSD.