First spotted years ago (https://github.com/dasch-swiss/knora-api/issues/231), and I just ran into it again by chance.
On the paper, it looks like they have come a long way from 2016. They also support CIDOC-CRM and some name authorities.
WISSKI, a german VRE using also ontologies
Do you know anyone that is involved in its development?
They say they tried different triplestores. That seems interesting.
Nope 
I just found them by chance