The API for Applied Energistics 2. It is open source to discuss changes, improve documentation, and provide better add-on support in general.
Development and standard builds can be obtained Here.
When compiling against the AE2 API you can use gradle dependencies, just add
dependencies { compile "appeng:appliedenergistics2:rv_-___-:dev" }
or add the compile line to your existing dependencies task to your build.gradle
Where the __ are filled in with the correct version criteria; AE2 is available from the default forge maven so no additional repositories are necessary.