Variations on this implementation are meant to be considered for inclusion in the Zope core sometime in the future.
NOTE! Zope 2.5 and better ships with sessioning technology based on CoreSessionTracking, so it needn't be installed on Zope 2.5 or better. However, the Zope 2.5 sessioning technology doesn't share an API with CST. If you've already started to develop using CST on older versions of Zope but you want to upgrade to Zope 2.5, CST is installable on Zope 2.5. You should try to migrate your code to the Zope 2.5 sessioning machinery when possible. CST will be maintained until its next release, 1.0, at which time it will likely become unmaintained.
For more info, see The Core Session Tracking Fishbowl Project.