Modern applications are highly connected applications, often consuming several asynchronous or stream-based services. This makes users happy, but can easily lead to code that is a nightmare to develop and maintain. Enter Reactive Extensions, also known as Rx. Rx can help tame callback hell and can abstract away the notion of time, turning asynchronous requests into observable sequences. Just as we can query normal sequences such as collections, these observable sequences can be composed through either standard query operators (e.g., filter, project, aggregate) or even temporal ones (e.g., “sample a noisy event stream at 100ms intervals”). In this talk, we’ll cover the JavaScript, .NET, C++, Ruby and Python and even RxJava. Use Rx wisely, and may your web service never be crashed by the weight of its own popularity!