Modern functional programming in a concurrent context often uses an effect system to model functionality. A functional effect system leverages the language’s own compiler and type systems to model concerns like I/O, parallelism, error handling, but can also extend to resource safety and dependency management. On the JVM within the Scala ecosystem, ZIO is a popular choice. In this presentation, we’ll first take a look at some of these concerns and see how they are addressed by plain Java, ZIO with Scala, and others. Once we’ve established the holistic solution ZIO can bring, we’ll explore how this can also help us develop and model high-quality front-end applications. We’ll demonstrate a real-time interactive whiteboard developed in this way.