Samsung
The Samsung Z.
Tizen is an open source operating system Samsung has spent a lot of resources developing along with a handful of other partners. In a way, it's Samsung's homegrown OS, like Apple's iOS. Many see Samsung's investment in Tizen as a way for the wean itself off its dependence of Google's Android.
The new Samsung Z will only be sold in Russia at launch, but it's Samsung's first step into exploring a new mobile operating system. If it takes off, you can expect Samsung to sell more Tizen handsets in other emerging markets where Android hasn't taken hold quite yet.
By using Tizen, Samsung doesn't have to worry about promoting Google services like Google Maps, Gmail, and the Google Play store for apps, movies, and books. Instead, Samsung can push its own services without having to give up potential revenue to Google. It's a big bet, but if it works, Samsung could one day use its own OS for future devices instead of Android.
At first glance, Tizen looks a lot like Android. In fact, the "skin" Samsung uses is almost the same as the skin it uses when it modifies the Android software for its Galaxy line of phones.
The Samsung Z has a 4.8-inch screen, which is slightly smaller than the 5.1-inch screen on the company's flagship Galaxy S5 phone. But it's still larger than the 4-inch screen on the iPhone 5S. The new phone also has some of the new features first introduced in the Galaxy S5 like ultra power saving mode, which can add hours of extra battery life, even if you only have a ~10% charge.