Knowledge Forum 4.0
Knowledge Forum 4.0 took the radical direction of being web-only. We'd had some support for web access by virtue of a perl program that used the client's communications protocol to talk directly to the server, but perl wasn't pre-installed on Mac OS (Classic) or Windows, and it had some performance problems. So we ported the perl software to C++ and incorporated it into the server directly.
For a time we had native client and web access running simultaneously, but never in a released version. The 3.x client remains buildable as of May 2006, but still talks only to a 3.x server.