Generative AI will exponentially increase humankind's productivity over the next 10 years. At the heart of this increase will be businesses simulating and generating complex insights in real-time. This will require digital twins at a scale and speed we've never seen before. ZefHub is a digital twin platform for developers to persist, sync, and stream data in real-time across space and time. Developers can build and maintain a foundational data and “information substrate,” to power simulations, what-if scenarios, optimizations, predictions, and more. ZefHub harnesses the open source library Zef, a toolkit for graph-relational data across time. It provides the building blocks, including a graph-relational DB, a Python DSL, and more, to develop distributed, reactive backends. Time travel to any previous state, work directly in Python (no separate query language), and query/traverse without the need for multi-join SQL queries. Visit the Zef GitHub repo: https://github.com/zefhub/zef