You don't have to do anything special from most WWW clients to access other information servers directly. Most clients have the protocol built in - for example Mosaic understands the FTP protocol, the TELNET protocol, Gopher, WAIS, NEWS, and local file access.
Of course, many of these will become obsolete as people design better gateways from servers, freeing up the clients to concentrate on clean efficient handling of HTTP, MIME and HTML. The rise of proxy servers such as CERN's httpd 3.0 mean that even a pure HTTP client could have access to FTP, GOPHER and so forth.