Earlier quoted context omitted.
Sandia seems to have some form of kernel, but only Federal-associated entities can get access to it. It would be interesting to see if they would license that out further for some amount of money.
If you're referring to Cubit, they license the ACIS kernel under the hood.
https://github.com/sandialabs/sgm
Originally open-source, but since taken back in-house. As I understand, which should not be construed as an accurate accounting, Sandia wants to flesh out the basics further before (potentially) open-sourcing it again.