LibraryThing.com is website which allows library enthusiasts to create their own online library catalogues. It also hosts a growing selection of historic collections which were owned by famous people.
The catalogues range from early modern times to the (almost) present. Some early modern examples include the libraries of Marie Antoinette (736 books), Thomas Jefferson (5,419 books), the Mather Family (1,814 books), and Mozart (41 books).
A list of the libraries added and completed so far is available here:
A list of Libraries in Progress is available here which includes details of how to get involved in the projects: