GATCO TRI-SEPS Serrated Edge & Point Sharpener.
It has a sharpening side for non-serrated knives.
And a side for serrated knives.
This is how the product is described in the website where I ordered it.
"Designed to be used by the armed forces, this triangular shaped, portable ceramic sharpener has a built-in angle guide to quickly restore a razor sharp edge to serrations, plain edges, entrenching tools, scissors, darts, fish hooks, ice picks, and other pointed instruments. The unique triangular design features two radius sizes and provides sharpening for large and small serrations. Includes a military-spec bead chain and clasp."
All in all, it's convenient to bring along in the field because its small and great for re-touching you knife wherever you are. But for really dull knives, in my opinion nothing will beat a carpenter stone or a wet sanding paper.
That's all folks! Thanks for reading.