Reactive Extensions (Rx)

The Reactive Extensions (Rx) is a library for composing asynchronous and event-based programs using observable sequences and LINQ-style query operators. Using Rx, developers represent asynchronous data streams with Observables, query asynchronous data streams using LINQ operators, and parameterize the concurrency in the asynchronous data streams using Schedulers. Simply put, Rx = Observables + LINQ + Schedulers.

Source: https://msdn.microsoft.com/en-us/data/gg577609.aspx
Date: 2011

Found some really useful extensions for C# async programming, namely IAsyncEnumerable/IAsyncEnumerator

GitHub dotnet/reactive