Kappa is an offshoot of <a href=https://www.ponylang.org/>Pony</a>.
Pony has some of the properties we need.
The term “reference capability” plays a critical role in
<a href=http://drops.dagstuhl.de/opus/volltexte/2016/6099/pdf/LIPIcs-ECOOP-2016-5.pdf>Kappa</a>.
<a href=https://2016.ecoop.org/event/iwaco-2016-first-paper-kappa-insights-current-status-and-future-work>too</a>
<p><a href=http://uu.diva-portal.org/smash/get/diva2:1164769/FULLTEXT01.pdf>Thesis</a>
<hr><a href=http://wrigstad.com/>Wrigstad</a> and his student <a href=https://eliasc.github.io/>Castegren</a> are developing Kappa.