Not sure how active is it but Genode looks interesting: https://genode.org/about/index https://genode.org/about/index "The Genode OS Framework is a tool kit f

Not sure how active is it but Genode looks interesting: https://genode.org/about/index https://genode.org/about/index "The Genode OS Framework is a tool kit for building highly secure special-purpose operating systems." "Genode is based on a recursive system structure. Each program runs in a dedicated sandbox and gets granted only those access rights and resources that are needed for its specific purpose."