Angular packages

@angular/core:  Provides essential pre-defined decorators, classes, interfaces and modules that are needed to run every angular application.
Example: @Component, @NgModule, @Pipe, @Directive, @Injectable, @Inject, NgZone, OnChanges, OnInit, ApplicationModule etc.

@angular/common: Provides built-in directives that are useful for most of the real-time applications.
Example: ngIf, ngSwitch, ngClass, ngFor etc.

@angular/compiler: Compiles "templates" (html code) into "javascript code".

@angular/platform-browser-dynamic: Invokes the angular compiler (JIT compilation) and specifies the startup module and also start executing the application.

@angular/platform-browser: Provides a set of pre-defined classes that are related to DOM and browser interaction.
Example: BrowserModule.

@angular/forms: Provides necessary pre-defined classes that are related to are needed to create and execute angular forms.
Example: FormsModule, ReactiveFormsModule, Validators, ngModel, ngForm etc.

@angular/router: Provides necessary pre-defined classes that are needed to create and execute angular routes.
Example: RouterModule, Routes, ActivatedRoute, CanActivate, routerLink etc.

@angular/animations: Provides necessary pre-defined classes that are needed to create and execute angular animations.
Example: BrowserAnimationsModule, animate, state, style, transition etc.

@angular/http: Provides a set of pre-defined classes that are needed to create and execute REST-API calls using AJAX technique.
Example: HttpClientModule.

@angular/cli: Provides necessary pre-defined commands that are needed to create, compile, build, add items in angular applications.
Example: ng new, ng serve, ng build, ng test etc.

rxjs: Provides necessary pre-defined classes for creating Observables, which are needed to represent the response of REST-API calls of AJAX.
Example: Observable, Observer, Subject etc.

zone.js: Provides necessary pre-defined classes for executing "change detection processes", while executing angular app.