Thank you, OP and everyone else who's commented. This is super helpful to see. It's great to learn about Nick's work specifically and as an introduction to the those working in this field - and to see the other helpful links everyone has posted.<p>I wrote a library to implement (most of) the Space Groups in the visual programming environment Grasshopper, which is inside 3d modeling software Rhino3d. This was to get architects working with 3d symmetries, not just 2d; and to get architecture students learning the spatial symmetries in more rigorous and complete ways. The scope and aim are completely different than these engines. But I'm hoping to rewrite it into a standalone program soon, so it's very helpful and timely to get this influx of information I hadn't sought out before!