The Amazon S3 Java toolkit by Amazon aims to simplify interaction with Amazon S3, part of Amazon Web Services. It also works with Amazon CloudFront. This library has been designed to interact with the API, that offers the features of storage, cloud, data backup, and disaster recovery. Available for download. The repository JetS3t for developers is an open source site for Amazon Simple Storage Service (S3).
Roll-your-own API service Usergrid has been acquired by API management company Apigee. Usergrid could potentially help Apigee reach out to mobile developers increasingly finding themselves needing APIs to interact with their apps. It's part of a trend of developers not only being API consumers, but also API providers--at least privately to their own apps.