The microdonation service Flattr is currently working on a REST API for accessing the flattr account. I have created a Java client called flattr4j, which makes accessing the API easier.
The client also supports the Open API and JavaScript API via a JSP taglib, as well as Maven and Spring. As long as the Flattr REST API is not public yet, you need to send a proposal to Flattr.
Have fun trying it out! Your feedback is welcome.