As far as I am aware, Apple does not seem to have a policy preventing this type of work. There was a fairly well-publicized release of an experimental codebase

As far as I am aware, Apple does not seem to have a policy preventing this type of work. There was a fairly well-publicized release of an experimental codebase from Ericsson: http://labs.ericsson.com/apps/bowser http://labs.ericsson.com/apps/bowser, which has since been retired (although as far as I know, not due to any conflict with Apple): http://labs.ericsson.com/blog/retiring-bowser http://labs.ericsson.com/blog/retiring-bowser.