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 try and throw and a wealth of new -errorcode values enable far more precise trapping and handling of exceptions with a familiar construct.
Tcl delivers in the pkgs subdirectory a bundled collection of third-party packages built and installed along with Tcl.
A thread-enabled default build, a bundled Thread package, and new command interp cancel make Tcl 8.6 ready for your multi-threaded programming tasks.
TDBC, SQLite
The socket command now recognizes numeric IPv6 addresses as valid values for its $host argument where platform support exists.
New command zlib provides utilities to handle compression of data and streams.
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.