A forum engine written in Java. Its architecture supports plugins and therefore is extensible. JCommune is integrated with other JTalks apps and thus if you like you can use either forum as a standalone app or install it together with Antarcticle and have same users being able to leave questions and write articles.
An article engine written in Scala. Very nice and cozy. Antarcticle can as well be run as standalone app or live together with JCommune and have same users being able to write articles and leave questions.