You can draw ERDs using GraphViz records. That will not trak/organize your metadata, geneate your DDL or anything else for that matter - but it will give you an entity relationship diagram that you can easily edit/update.
It will handle all the layout/arrangement details of the diagram for you. It does a pretty good job of this. It is sort of a declarative diagram-drawing language. Very simple to learn. Requires nothing but a text editor to use. Many applications use its abilities behind the scenes to generate their diagrams also.
