Amazon S3

Amazon S3 is a cloud-based filesystem offered as a paid service by Amazon. It allows storage of Web-accessible objects which can be operated on via an API. Some competing services have emerged which use a compatible API, allowing users to freely switch services without modifying programs based on accessing the files via an API, with only server hostnames needing to be changed in the program code.

Links

 * Official site
 * Wikipedia article
 * Ceph Object Gateway S3 API
 * Dreamhost DreamObjects, a competing service that is API-compatible