When researching ancestors in the area of Belgium and Luxembourg, “Dénombrements” that have been preserved in the Archives of Luxembourg are a gold mine of information. You might think of these enumerations as a kind of census. You can find names, but you also get great detail about the condition of the people mentioned.
The catch is that digital images of these exist, but they aren’t indexed. They have to be read, and the handwriting used is a style of cursive that takes time to learn. I have been practicing, with the help of the genealogy community online, and present here an excerpt of that translation.