This software paper introduces Oceananigans as a Julia framework for geophysical fluid simulations on CPUs and GPUs. It combines a high-level scripting interface with numerical methods for incompressible, stratified, rotating flow. Users can specify model configurations and diagnostics while sharing a common code base across hardware architectures. The paper describes performance benchmarks, verification practices, and applications such as ocean boundary-layer turbulence. Readers get a concise introduction to the software’s original capabilities and design, helping them assess it as a platform for numerical experiments.