What is LibraryThing?
LibraryThing is an online service to help people catalog their books easily. You can access your catalog from anywhere—even on your mobile phone. Because everyone catalogs together, LibraryThing also connects people with the same books, comes up with suggestions for what to read next, and so forth.
What software does it require?
None. If you can read this, you can use LibraryThing.
What does it cost?
A free account allows you to catalog up to 200 books. A paid account allows you to catalog any number of books. Paid personal accounts cost $10 for a year or $25 for a lifetime. (See here for non-personal accounts.) I conservatively predict the revenue will enable me to recline all day on an enormous pile of gold.
And they have a blog... where they discuss new features, plans and announcements.Check out LibraryThing and consider adding the blog to your RSS Reader of choice.