AsyncSubject`1 Represents the result of an asynchronous operation. The last value before the OnCompleted notification, or the error received through OnError, is sent to all subscribed observers.

 BehaviorSubject`1 Represents a value that changes over time. Observers can subscribe to the subject to receive the last (or initial) value and all subsequent notifications.

 ReplaySubject`1 Represents an object that is both an observable sequence as well as an observer. Each notification is broadcasted to all subscribed and future observers, subject to buffer trimming policies.

 Subject`1 Represents an object that is both an observable sequence as well as an observer. Each notification is broadcasted to all subscribed observers.

 Subject Provides a set of static methods for creating subjects.

 SubjectBase`1 Base class for objects that are both an observable sequence as well as an observer.

 IConnectableObservable`1 Represents an observable wrapper that can be connected and disconnected from its underlying observable sequence.

 ISubject`1 Represents an object that is both an observable sequence as well as an observer.

 ISubject`2 Represents an object that is both an observable sequence as well as an observer.