Actually it's a LibraryThing - thanks and curses (mostly thanks) to Anthony Kendall for turning me on to this web site, the booklover's equivalent of crack (wait, I thought that was Amazon - OK, now there's two kinds). It's a place to easily create a database of books, either public or private, and free for up to 200 books. Since I spent about 90 minutes between last night and this morning and entered 158 books without breaking a sweat, I figured I should support the developer and become a $25 lifetime member.
As I mentioned in an early post about obsession, every obsession phase (flying, songwriting, physics, optics, Japanese, space, whatever) has been accompanied by books. Since I rarely get rid of a book, that means there are quite a few around my house and office. I don't know how many, but maybe a couple of thousand. I have occasionally started to catalog them myself, but it's a slow job if you have to type or write down much information yourself. So I quickly lose interest (another problem is that if I open a book to grab information, there's a good chance I will get stuck reading it).
But LibraryThing is really easy and fast to use because it is linked to book databases at Amazon.com, the Library of Congress, and other sources of book information. So you don't have to enter much information to find and enter a book into your catalog. An even faster way is to find someone else who has a public catalog with some books in common with you (they tell you who these people are). Chances are he or she has others that you have. You can view galleries of book covers and when you see one you have, just click and select "add to mine." You can import and export catalog data; display books in various formats; add ratings, comments, or reviews; and probably a lot of other stuff. Way cool. My embryonic catalog is public if you want to take a look (go to LibraryThing.com, search for user FlyingSinger).