As with most manufacturers, the included OS is a version of Android – 4.4.4 – customised by the handset's maker, Xiaomi in this case. Xiaomi's included Android skin is known as MIUI, and the Redmi 2 comes with MIUI 6 – the latest version.
To make it clear from the beginning, MIUI looks very similar to iOS, but that's no bad thing. The comparisons begin with the modern, flat icons that Xiaomi have included, and the lack of an app drawer – which is rare for Android – continue this theme.
That said, MIUI is still Android, and this is evident when you swipe down and the familiar quick settings appear. Here, they are a clean white against a semi-transparent background.
Indeed, if MIUI is not to your liking, you can change it for another launcher, something you can't do within iOS.
It is worth mentioning, though, that by default the Redmi 2 doesn't include the Google Play Store. Rather, Xiaomi have their own app store included with the device.
As it is still an Android OS, you can install the Play Store anyway to access the usual collect of apps, but this has to be done using a computer. It's not a problem for most, it just means you'll find it hard to use the Redmi 2 out of the box.
On the whole, the OS looks like iOS but retains the Android customisability levels. It's beautiful and clean, and can be completely done away with it you don't like it.