Android, but not as we know it.
The Nokia X software is based on Android 4.1 Jelly Bean, but is heavily customised by Nokia and does not include Google services.
Strangely though, none of these replacement services are pushed on the user. Setting the phone up from new gives you a brief tutorial of the very basics of the user interface and that is it.
Nokia said that the aim with the X range was to be able to get first time smartphone users onto the Microsoft platform through a Microsoft account, but never once are you prompted to create one and the only Microsoft product pre-installed on the Nokia X is Skype.
Even more strangely, Blackberry Messenger is also installed out of the box, so Skype doesn't even have messaging exclusivity.
It is just as easy to open the mail app and connect to your Google account as it is to any other email system.
With the Nokia X being based on Android the mail app is the standard one that comes with most Android devices, albeit heavily skinned and restyled.
Nokia has provided some of its flagship services on the X including HERE Maps which are fantastic and allow you to download maps for offline usage. It works well, is reasonably fast and the GPS is as accurate as you would expect.
MixRadio is another great service allowing you to stream music or download mixes for offline playback. It is free with some minor limitations and is a great addition at this price point. The fact the speaker is loud is nice though it is very basic in every other sense.
The Glance screen, which shows the time and notifications when the phone is locked in a low power state, makes an appearance on the X as does the ability to double tap to wake the screen. Both of these features are brought over from Nokia's Lumia range of devices and are very welcome here.
The real selling point of the Nokia X though is the quality of the hardware given its price. It has a usable camera on-board and is a well-crafted device available at a lower price point than most smartphones. As a cheap entry point to smartphone ownership, it is a good option.