Mobius is an experimental code base whose implementation of B-splines is based on "The NURBS Book" by L. Piegl and W. Tiller. OpenCascade comes with different implementation of basis splines and geometries. Why we started Mobius back in the day was the idea to have full control over the basics. I wanted to stop being dependent on OpenCascade. OpenCascade lacks quite a number of surfacing operations, such as fairing, unstructured point cloud approximation, controlled skinning, even Coons patches are kinda questionable with it. In Mobius, our driving idea is to grow up an alternative open-sourced surfacing engine (without topology, so it's not a real CAD kernel) that would stay compatible with OpenCascade.
As of now, this library is quite rudimental and I wouldn't advice you plugging it in unless you have a good reason to do so. Among operators that work in Mobius, I can name surface interpolation, approximation, fairing, and some basic operations with meshes. So take it as R&D and do not rely on it in somewhat critical scenarios.
We want to keep developing fundamental algorithms, and we need a code base for these experiments. At the lower level (CAGD), it is Mobius. At the higher level (CAD) it's Analysis Situs. And we don't contribute to OpenCascade as such for a plenty of reasons.