In a research project, the Mannheim University Library digitized several German municipal directories from the period between 1880 and 1976. The publication contains historical population censuses and population surveys at municipal level from the German Reich, the FRG and the GDR. A full text search is available by processing the scans with OCR software.
The digitised collection of the FDZ can be used freely. Further information can be found here: Public Domain Mark 1.0.