By maturity I meant something like "continuous opeartion for a year with cryptographically signed live update (including cryptography themselves, implemented in VM)", which Urbit did. But okay, I am also interested in competing projects of any maturity.

Because implementing cryptography in a bespoke VM is an important feature? Why? That's the kind of thing cryptography engineers try to avoid.

You haven't named even one competing project. I think it is a good justification for interest in Urbit.