There seems to be two types of bindings currently in common use. The old three pin ones are definitely not cool anymore?
NNN bindings use a short metal rod in the toe of the boot which connects with a corresponding clip-in binding on the ski. In addition to the toe binding, NNN bindings also include a series of matching ridges on the boots and ski for greater grip and control. Several skiing disciplines take advantage of NNN bindings because they are easy to use and provide great flexibility for the skier. NNN bindings include a safety release so that if a skier falls, he or she will not become entangled with the skis.
NNN bindings allow freedom of movement for the heel, which is a crucial part of cross country skiing and telemark skiing. The skier can lift his or her heel entirely out of the binding but still be firmly connected at the toe. When solid lateral traction is needed, the skier can place his or her heel flat on the ski and connect with the ridged features of the binding.
Another company, Salomon, makes a binding system similar to NNN bindings. The Salomon Nordic System (SNS) bindings are also constructed with a binding rod and ridges. However, the layout of the SNS binding system is slightly different. Therefore, boots and ski bindings designed for SNS use are not compatible with NNN bindings.
I have tried both and find no noticeable different between them as far as how well they work. I am sure the manufacturer's would argue specific points, but they both work well.
The main point to know is that your boots and bindings must be compatible. NNN boots do not work with SNS bindings and vice versa.