JSONiq specification, which specifies two subtypes of languages: one that hides XML details and provides JS-like syntax, and one that enriches XQuery syntax with JSON constructors and such. Zorba implements JSONiq.
Corona, which builds on top of MarkLogic provides a REST interface for storing, managing, and searching XML, JSON, Text and Binary content.
MarkLogic 6 and later provide a similar REST interface as Corona out of the box.
MarkLogic 8 and later support JSON natively in both their XQuery and Server-side JavaScript environment. You can apply XPath on it.