Many projects have come and gone and some are still active, but we are unaware of any actual technical publications, white papers, or implemented systems that can work securely between any pair of chains. Also there are none that address the full range of functionality needed for a comprehensive user experience. Moreover the actual performance in terms of executed trades has been patchy at best

Some of the potentially relevant projects that we are aware of include: Bancor, OasisDEX, Switcheo, WhaleEx, Yolo, komodo, Block DX, REN.