A delta virtual filesystem appears to be related in some way to trsync. Delta calculation for the template framework and filesystem based on vfs by Stephen Huntley.
[more info on how to use this?]
LV ActiveTcl SPARC Solaris patchlevel 8.6b1.1 - provided as a ActiveTcl 8.6 beta back in the good old days.
% package require trsync couldn't read file "/tmp/.lwv/ActiveTcl-8.6.0/bin/base-tcl8.6-thread-solaris-sparc-2.8/lib/vfs/template/tdelta.tcl": no such file or directory
I don't have a currently supported platform on which to test this.