What is Angular 4 and from where I can learn more about it?

Question

Recently someone told me about Angular 4, what is it? How is it different from Angular 2? I am learning Angular 2. I tried to find the official website of Angular 4 but I didn't get the result. I am very curious about it.

EDIT

Angular 4 website is now available here.

EDIT 2

Angular 5 (beta) is now available here.

EDIT 3

Angular 5 is now available here, the changes are available here

EDIT 4

Angular 6 is now available here.

EDIT 5

Angular 7 is now available.

EDIT 6

Angular 8 is now available here.

For updates and new features, please visit Angular blog post for version 8

Edit 7

Angular 9 documentation can be found here https://next.angular.io/docs

For updates and new features, please visit Angular blog post for version 9

Answer 1

Angular 4 is just a newer version of Angular than Angular 2.

Angular 2.x.x, and Angular 4.x.x are also named Angular, while the previous version (1.x.x) is named AngularJS.
This name difference indicates that there are major differences, while Angular 4.x.x is only a newer version of Angular than Angular 2.x.x is.

Angular uses semantic versioning since Angular 2, which requires the major number being increased when breaking changes were introduced.

The Angular team postponed features that cause breaking changes, which will be released with Angular 4.

Angular version 3.x.x was skipped to be able to align the version numbers of the core modules, because the Router already had version 3.

To see what changes will be introduced in Angular4 see https://github.com/angular/angular/blob/master/CHANGELOG.md

See also this blog post http://angularjs.blogspot.co.at/2016/10/versioning-and-releasing-angular.html