3.3 at the moment

OK, sorry for not digging enough before asking, this seems to be handled by Elgg now in core with Access Control Lists.
I suppose I'd need to write something that makes an ACL right from the entity edit page with the user I want to give access to.

The friends_collections plugin is a nice start to see how it's done but it's kinda an overhead for users to first friend the other user, make a special friends collection with them, then go to the entity and change the access to that friendscollection.

I'm gonna try to make something that does all that right from the entity editpage with a userpicker.

https://github.com/beck24/granular_access

https://github.com/hypeJunction/elgg_tokeninput

https://github.com/jumbojett/vroom