My personal library contains a few thousand books. When your library reaches such a size, it becomes obvious that at least a little organization is necessary, and so I have, over the years, aimed to maintain a catalogue, or at least to keep it all organized. Very early on, I tried using some desktop software for the purpose, including Book Collector from Collectorz.com, and some linux app which I've forgotten, but these didn't work out.
By 2007, I was looking for a good online solution. I tried Google's library feature, but it wasn't well-suited for physical libraries. Starting in 2011, I put most of my fiction, and some of my nonfiction, into Goodreads, but it too isn't great as an actual library catalogue (though it's okay for social aspects, like reviewing books). By 2014, I landed on LibraryThing, which I've been pretty happy with.