erd2db

I am looking for a tool in which I can create a nice erd diagram with all the relations and then this will output SQL, ruby migrate syntax or what ever. There is something like this called toad but there is nothing open source. Further there are some dia converts that take in some dia pic and convert it to something, but this doesn't work. So please would someone write something like this.
http://en.wikipedia.org/wiki/Comparison_of_database_tools