Elda is a Java implementation of the Linked Data API, which provides a configurable way to access RDF data using simple RESTful URLs that are translated into queries to a SPARQL endpoint. The API developer (probably you) writes an API spec (in RDF) which specifies how to translate URLs into queries.
Elda is the Epimorphics implementation of the LDA. It comes with some pre-built examples which allow you to experiment with the style of query and get started with building your own configurations.
See the quickstart documentation. For summaries of the latest releases, see the documentation root.