Explore the evolution of declarative workflows in this comprehensive conference talk, starting from Rx.NET observables and async enumerables, and tracing their development into the multi-platform standard known as reactive streams. Delve into the internals of Akka.NET streams, an implementation of this standard, and discover how streams can be utilized as universal building blocks across various domains, including networking and event sourcing. Learn about API vs SP tradeoffs, design decisions in reactive extensions, limitations of async enumerables, and the publish-subscribe model. Examine concepts such as dynamic push-pull demand, materialization processes, and the interpreter pattern. Gain insights into server-side extensions, flow synchronization, and persistence through practical demonstrations and examples, including a beautiful flowgraph DSL.