N3

N3 is a notation designed to make writing RDF easier. (For those who don't know offhand, RDF is a standard for encoding predicate data in XML).

N3 has some interesting features. For example, it views the "." operator in OO languages as a graph traversal operator, and then promptly provides a "^" operator that traverses the graph in the opposite direction -- something that OO languages cannot do because of the underlying memory model of references and pointers.

Perhaps the most interesting thing about N3 is that it's a notation for a predicate-based data store, designed by someone whose apparent background is closer to C++ and Lisp than to Prolog. As such, it takes concepts from C++ and Lisp and mutates them in ways that force the programmer to think of those concepts in a very different light.