Yep, but it is not easy problem, I don't know any existing app that does it well. The thing is that really useful tool would implement several types of referenc

Yep, but it is not easy problem, I don't know any existing app that does it well. The thing is that really useful tool would implement several types of referencing, because there are several equally important ways for doing it, i.e. sometimes I need to have just an arrow pointing from reference to destination, sometimes I want a tag, which after clicking on will embed destination in reference place, sometimes I want just some kind of preview.