Using this page to "crowd-source" some text for http://www.tcl.tk/software/tcltk/8.6.html .
The commands of the TclOO package are now part of Tcl itself. This gives Tcl a built-in object system that is fully dynamic, class-based, and includes advanced features such as meta-classes, filters, and mixins.
New version 4 of the popular package Itcl (aka incr Tcl) is also included, granting support for some traditional OO Tcl programming out of the box as well.
New commands lmap and dict map enable the elegant expression of transformations over Tcl containers.
New commands chan push and chan pop expose the power of stacked channels without the need to write C code.