This is a German proofed 9mm pinfire revolver by an unknown maker. The German pinfire guns are much less common that the Belgian or French ones.
It is mechanically sound and works in double or single action. It has its extractor rod and loading gate intact. The only mechanical issue is that the spring for holding the loading gate closed is partially broken to where you need to use a small knife or similar to press it as fingers will not fit under there. You could also just remove that little spring or replace it as the little screw under the loading gate is accessible.