ProjecturEd is a general purpose projectional editor written in Common Lisp.
It supports the integrated presentation and editing of arbitrary domains. The edited data is represented in their natural, domain specific data structures (as opposed to a flat string of characters), which accommodates for the implementation of many interesting, but yet to be explored features of structured editing.
It also supports multiple projections of the same object, and thus it can simultaneously provide different notations, potentially all of them editable. These views can be textual or fully graphical, are easy to add to the framework, and due to the architecture they combine well.
from the profile of Levente Mészáros (projectured)