Thanks to Michael Frederiksmose for the tip: Netscape Communications has released the first beta of its Communicator 4.5 suite of Web software. I installed Communicator 4.5 last night and, surprisingly, it didn't totally overwrite my 4.05 install; it did, however, change all my 4.05 shortcuts to point to 4.5.
Communicator 4.5 adds a number of new features, including a 3-pane mail and news interface in Messenger that's reminiscent of Outlook Express, a new Calendar, and a "Related sites" feature in Navigator that's supposed to alert you of Web site similar to the one you are currently visiting. Be advised that this is a preview release and the software expires on October 15th.
For more information on Communicator 4.5, visit the release notes page.
You can download the suite directly from the Netscape FTP site