Buildr is a simple and intuitive build system for Java projects. After 10 months of development and a lot of positive feedback, it will be incubated by the Apache Foundation, which will be opening its doors to its first Ruby project.
Maven 2.0 recalcitrants have been looking for alternatives with less XML and easier plugin development. Buildr might be the solution, and even boasts faster performance than Maven!
Maven is a pattern-based build framework for Java and J2EE projects; more than just scripting builds for arbitrary projects, Maven knows about J2EE, Struts, Hibernate, etc. and has a prescribed way of structuring and organizing a project from its moment of creation through testing, packaging, and deployment.