We're a large backup vendor so honestly I've had the budget, expertise and time (from backup ventures unrelated to Era which is a community project) to build our own digital twins from scratch that e.g. run SOQL and implement the full API.
Since we have backup offerings at Eon we have the excuse to build really good digital twins for our software factory and the sketching algorithms and data engineering/science experts to make the data realistic.
This was definitely more "reinventing the wheel" than reusing a projects - Era is optimized for reads and a lot of data, we stream/read everything from a datalake so state is mostly immutable and we don't have to worry about e.g. collecting personal user information or scale too much.
The hard part here is obviously the very long and expensive estate generation for companies rather than the digital twins (that are interesting and million of lines of code but less exciting to the scientist in me. If the rsearch is interesting lmk and I'll send the papers over.