System 3.4, Finder 6.1 (AppleShare 2.0.1 Work Station)
System 3.4 was released in early 1988 with the AppleShare 2.0 package for the Macintosh 512Ke, long after System 4 was complete and just prior to System 6 being released. It appears that its only purpose was to add AppleShare 2.0 support to System 3 in a way that could run on the Macintosh 512Ke.