What is the Gradle counterpart to Maven archetypes? How can I give other Gradle users a template for the file and directory layout for a new project?
Use build init plugin:
~$ mkdir newproj
~$ cd newproj
~/newproj$ gradle init --type java-library
At the moment java-library, scala-library, groovy-library, java-application, pom and basic supported. The feature is incubating, thus it can be changed in future releases, so keep an eye on docs. 
Looks like solution is available now: https://plugins.gradle.org/plugin/com.orctom.archetype
Gradle doesn't support this (yet). There's a open feature request opened already.