From their site: Google Checkout is a checkout process that you integrate with your website, enabling your customers to buy from you quickly and securely, using a single username and password. Once they do, you can use Google Checkout to charge their credit cards, process their orders, and receive payment in your bank account.
The following is a list of SDKs from our SDK directory that matched your search term. Though your definition of an SDK may differ, in our world, we define SDKs as platform- specific tools for consuming existing APIs of the sort we list in our API directory. For example, the Ruby SDK for consuming the Twitter Ads API. If you think an SDK, API, or other asset is missing from our directory, be sure to check our guidelines for making contributions to ProgrammableWeb.