React is a UI-focused Framework for those who want seamless website integration relating to view aspects. It results in ultra-fast rendering, which makes it perfect for websites that rely much on interface in order to draw in its audience. React was developed by another tech giant Facebook, and is meant to be an open source Framework.
Then we have Ember, which is an open source Framework made by Yehuda Katz. This particular Framework works much like React in that it is also UI intensive. However, this one has the advantage of a rather huge and extremely active community, which will provide you with all of the support you need if you ever run into any trouble. If you want better performance, it is best paired with Fastboot.js.