It's split between three big players this year: Samsung, LG and Sony.
Pictures explain better than words. See what HZO does to a bare Raspberry Pi.
In The News
"Bare" Android is no longer trendy. We have choices now: Tizen (from the Linux Foundation,) Firefox OS (I guess you know where it is coming from) and Ubuntu OS. Below you can see videos of Firefox OS and Tizen. After playing with more than 20 different devices, I wasn't able to unlock the Ubuntu OS device. There goes great usability.
A relatively obscure Chinese company, Oppo has just launched its N1 mobile phone, to complement its Find 5 device. With 2 GB of RAM and a Quad Core Snapdragon, it packs some serious punch. It features a custom Android version named Color OS. It felt as one of the fastest phones at this year's Mobile World Congress. You can see a video below.
Nokia astonished the mobile world (well, more or less since news of this had already been leaked) with its Nokia X1, an Android phone that makes Nokia probably the first mobile manufacturer to have 3 operating systems under control. X1 is a relatively heavy UI change on Android, but as a phone it felt relatively vulgar, indistinguishable from any other Android phone. Below you'll see a few pictures.
We've had the pleasure of checking out the fresh-from-the-oven Sailfish OS 1.0, living inside the new Jolla handset. Sailfish is a new mobile operating system, cross-compatible with Android (so you'll be getting Angry Birds, don't worry.) Sailfish feels snappy and fast, and its swipe around menu system is surprisingly smooth. You can see a few pictures and a video below.