Ruby (programming language)
Ruby has been described as a multi-paradigm programming language: it allows procedural programming (defining functions/variables outside classes makes them part of the root, 'self' Object), with object orientation (everything is an object) or functional programming (it has anonymous functions, closures, and continuations; statements all have values, and functions return the last evaluation). It has support for introspection, reflection and metaprogramming, as well as support for interpreter-based threads. Ruby features dynamic typing, and supports parametric polymorphism.
Apache Buildr
Though Buildr's general philosophy is similar to Maven, it uses Ruby's scripting possibilities to provide a more flexible and customizable programming model. The user writes a Ruby build script, declaring a project, its sub-projects, artifacts, dependencies, packaging rules, etc. Based on these declarations, a list of standard targets are provided to compile or package the project, upload a prepared package to a remote repository, clean up the build results, run tests and so on. Hooks are provided to execute custom Ruby code before or after the standard targets, allowing the user to comfortably override any defaults and further specify the behavior of the standard targets. New, completely user-written targets can be added.