The following Google services provide APIs that implement the Google Data Protocol.
Each API has its own set of guides and resources, including information about using client libraries. If you're trying to accomplish a certain task with an API, the Developer's Guide for that API should point you in the right direction. Most APIs also include code samples and other easy ways to get started.
Warning: Several of the APIs listed on this page are deprecated or obsolete, and some have been replaced with APIs that aren't Google Data APIs.