Composite builds are a way to join multiple independent Gradle builds and build them together.
This looks really promising. It will encourage to create plugins and modules. Thus, less coupled applications. The Groovy ecosystem will leverage it for sure. Many of the projects ( Grails, Ratpack, Griffon ) can use Gradle as their build system and use plugins or modules.
Moreover, IntelliJ IDEA already supports Gradle Composite builds.
If you are creating documentation with Asciidoctor, you will find the collection of examples on how to use Gradle and Asciidoctor to create html5, pdf, epub, deck.js, and reveal.js outputs really useful. Courtesy of @lspacewalker and @rob_winch.
At work I generate either html5 and pdf but I am curious to test the epub output.