The major version number grow reflects that X11 is updated to version 7.1, which is a very structural modification, system wide. All X-software have been recompiled, including a large amount of software in the ZenCommunity repository. This is the biggest change since the beginning of the Zenwalk project, however, old Zenwalk 3.x and Slackware 11 X-software packages should be compatible with Zenwalk 4.0. Upgrade has proved to be possible as many testers succeeded in the migration : average users are still recommended to do clean/fresh installs.
Tools and Utilities
Product page: here