Poul, have you looked at the Mill Architecture? It doesn't provide capabilities but provides "turfs". A turf is a set of [base..limit) regions in a single address space. Threads within a turf can only see what the turf allows them to see. Regions can be shared between turfs if so desired (& how one may communicate large amounts of data). When a thread makes a "portal call" it is in another turf and can only see what is in that turf (+ call args, passed on the "belt"). Not clear if this will go anywhere & might get forgotten but it is an interesting architecture worth exploring.