METAOBJ is a large metapost package providing high-level objects. It implements many of PSTricks' features for node connections, but also trees, matrices, and many other things. It more or less contains boxes.mp and rboxes.mp. There is a large (albeit not complete) documentation distributed with the package. It is easily extensible with new objects.

The author is Denis B. Roegel. The package is Copyright © 2001-2006 D. Roegel.