"Schienendrilling" = any Drilling, even larger bore ones, with the rifle barrel on top of the shot barrels, inside the "Schiene" = top rib.
"Waldläufer" = woodsloafer, originally a trademark of Schmidt & Habermann, Suhl, ESHA. ESHA offered such Schienendrillinge since about WW1. The Waldläufer was intended for fur and feather, the small bore rifle barrel giving some added reach for an occasional fox. Originals by ESHA were usually double 16 bores with a .22lr or 5.6x35R Vierling on top. The Vierling cartridge was sort of a parallel development of the .22 Hornet: The Germans took the .22 Winchester centerfire case and loaded it with smokeless and jacketed bullets nearly to later Hornet ballistics. In due time "Waldläufer" became a generic term or household word for all these small-bore Schienendrillinge, regardless of maker. The development of small-bore, rifled insert barrels for shotguns by Burgsmüller and Krieghoff deeply cut into the appeal of the Waldläufer, as they solved the same "problem" at a much lower price.
After WW2 Waldläufer were only offered on order by Ferlach makers, but these were sometimes even more unusual: I have once seen a Ferlach made double rifle in 9.3x74R with a .22 Hornet barrel on top.