I’ve been using this program for years. It’s a freeware “index card simulator,” which is very useful for organizing books, papers, and various other things. The free version is good enough for most people, but if you want more you can head over to the Products page and buy an “enhanced” version (20 dollars for the version without the extras).
p.s. Another good thing: The format this program uses to save files is a simple XML file. So, if a file gets partially corrupted, you can go into a plain-text editor, open the file, and strip away all the funny tags. It won’t be in order, but at least it’ll be there!