It's easy to think of many of the processes we work within as linear chains of cause and effect. Most of the time we are working within more complex systems where positive and negative feedback loops influence outcomes. Systems is a set of tools for describing, executing and visualizing systems diagrams. Using a compact DSL and running either standalone or within a Jupyter Notebook, it's super easy to describe fairly complex processes and the flow of information through them. It's pretty much a niche tool; but an interesting and fun one.