You can clone with
HTTPS or Subversion.
The idea is to add a level of indirection where 'package' can map to package-jar, package-war, package-ear, package-whatever.
fwiw, http://maven.apache.org/guides/introduction/introduction-to-the-lifecycle.html#Lifecycle_Reference has a list of at least some potential kinds of package that the maven 'package' can map to.
IMPORTANT This project has moved to https://github.com/sbt/sbt. This issue still exists to avoid dead links, but GitHub limitations prevent the original issue from being correctly preserved here. Please see sbt/sbt#156 for the full issue and to comment.