Glyphicus is an experimental application that allows scholars to explore a subject text, creating ad-hoc markup tags as they go. Glyphicus uses a stand-alone markup strategy, and a database back end, so overlapping, parallel and even contradictory tags are just fine.
It's like letting a hundred different people keep their own highlighting and marginal notes in the same book only nobody gets confused, and there's none of the headaches of XML encoding.