APIFinder is a growing index of various application programming interfaces (APIs). An API provides a set of instructions that you can use to make new software interoperate with existing applications. This site is also a place to share ideas and advice on how to use APIs in your programming. This site grows in part through community contribution so please submit your favorite APIs as well as articles and API-related projects today! I didn't find unAPI in their collection. I did spot ISBNdb, a tool for using an ISBN database.