I think it was mentioned in DX comments that it's linux. Other than that (I read a bunch of them and could be mistaken), I'm just presuming, since it's not windows CE. They'd mention that, but don't necessarily mention linux.
Also, here's a question to those with the machine: I read something about it not supporting all normal formats of Neogeo roms, is there a converter or do you have to hunt down some obscure format to use it? And how difficult is it to upgrade an emu? most of them come bundled with the machine, right? CPS-2, does it work or not? And does it support screen rotating for shooters? I bet the controls wouldn't be very comfy for that, but maybe I'm wrong.