What is a good free conceptual modeling tool for EER modeling?
It should support specialization, generalization, union, etc.
MySQL Workbench seemed to belong to the physical modeling stage (examples included VARCHAR or INTEGER specifications for attributes and it deals with tables rather than entities).
Open System Architect is brilliant.
SQL Power Architect .
It's community edition is free, and does a really great job helping you build your ERDs.
It works on Windows, Linux, and OSX.