A general site run by David Lamb at Queens University Ontario that provides some general information of CASE, including the ECMA reference model and links to a large number of CASE tool suppliers. Some short reviews of tools are also available. Some of the information is current but quite a lot of it hasn't been updated recently.
There are a number of open source CASE tools available through the open source repository sourceforge. I haven't experimented with them but, from their descriptions, they look interesting. They include:
CVS which is a very widely used version management system. Clients are available for more or less every platform.
UML Modeler which is a graphical editor for a number of UML models (not all).
UML2EJB which is a code generator that takes a UML model expressed in XML and generates EJB classes.