I was at a show last weekend and found this. I thought it was a joke at first, but it's real. From what I was able to find The Liliput was manufactured by Waffenfabrik August Menz in Suhl, Germany from approximately 1920 to 1927. And it's considered the second smallest center fire cartridge, Something called a Kolibri is the smallest.
I can't find any info on the bullet weight, or ballistics though. There isn't any head stamp either, if there were, I don't have a magnifying glass that strong.