When the German Empire was divided in many smaller Kingdoms, most of these Kingdoms had their own stamps. The issues
where not much different of those for other countries. The heads of the Kings were in most cases the topic of the stamp, and
there were some topics like animals, sport, statues.
When the German Emperor bought all the rights for postal delivery in Germany, the local postal services dissapeared.
Simply cause they were forbidden.
With new laws in the recent years Local Postal Services are allowed again, but like in Holland and many other countries,
delivery of letters is forbidden. Postcards, invitations, all other printed matter, packages, are ok.
And though many countries have such services, not all of them create stamps.
In Belgium, Denmark, Spain and France I know of Local postal services who deliver but don't have their own stamps.
(On the green stamp on the left, you see Karl May)
The new Citipost in Germany however, has also done its best to come with stamps that almost look like traditional German
stamps. Osnabrück has a beautiful serie with architecture.
As for Hannover, they chose for modern architecture. But I prefer the Osnabrück stamps over those from Hannover.