FREE Entity Relationship Diagram Software

Does anyone know of a free entity relationship diagram software?

My pencil and paper diagrams are getting rather elaborate and
overlapping and hard to update.

I used to use WO Modeler and it had an Entity Relationship Diagram tool
which auto synched with the DB and drew the relationships and allowed
you to see the model files in a visual way.

Cayenne was a off shoot of that ; if anyone knows of something similar
for ROR that would be sweet.