First off in the open-source bin we have Books which is book cataloging application to keep track of your library (requires OSX 10.4).
Secondly we have Cashbox a personal finance management application (requires OSX 10.4).
This one might prove a little tricky, i'm not sure but the instructions seem pretty straightforward and Home Media Librarian is a java application that uses MySQL database. It does what is says on the tin, catalogue your cd's, dvd's, records or music collection.
Now two freeware apps - eBook Library is an application developed to help you practice speed reading.
Luca is a fully featured and fully functional accounting application - snap it up, awesome freeware (requires OSX 10.4 Tiger)