Thanks!

Netscape Composer (released with Netscape Communicator) came out in 1997.

Adobe PageMill 1.0 was released in 1995.  Adobe acquired it when they bought Seneca.  Can't find anything on when Seneca initially released it.

Haven't been able to find an initial release date for PageSpinner.

There was also a Web Weaver Lite but haven't found a release date for that one either.