Please suggest tools for creating Class Diagrams with the following criteria:
Also, please only suggest the tools that you've actually used.
UPDATE: Please DO NOT include those UML Diagram tools that cannot create Class Diagrams.
I use GenMyModel, first released in 2013. It's a real UML modeler, not a drawing tool. Your diagrams are UML-compliant, generate code and can be exported as UML/XMI files. It's web-based and free so it matches your criteria.