The SMEStorage multi-cloud API has been used in a variety of tools. It is what is used in our iPad/iPhone, BlackBerry, Windows, Linux and Mac clients. From a language perspective this means Objective C, Java (J2ME), .net, Delphi, PERL, Ruby and of course HTML and PHP. The API is very rich and targetting this API means you can address over 10 storage clouds by binding to one API.
To see how easy it was to use for other users we gave the API to a company and asked them to create an Adobe Air mockup that used the API. What they came back with in a short space of time was impressive. You can download the Air client here. It is fully functional and supports a lot of of the functionality of the site.