In Fedora 21, TCL/TK has been upgraded to version 8.6.1, which includes numerous bug fixes and enhancements. The most notable of them are:
TCL 8.6
Support for IPv6 networking for both client and server sockets
Support for SQL Database - The bundled tdbc package which contains the Tcl DataBase Connectivity interface now enables writing SQL database-powered scripts decoupled from any particular database engine. The bundled sqlite3 and tdbc::sqlite3 packages supply a powerful and popular SQL database engine ready to use.
Support for Object Oriented Programming - The commands of the TclOO package are now part of the TCL language itself. This gives TCL a built-in fully dynamic, class-based object system and also includes advanced features such as meta-classes, filters, and mixins. A new version 4 of the popular package Itcl (also known as "incr TCL") is also included, now built on a TclOO foundation, granting support for some traditional Object Oriented TCL programming out of the box as well.
TK 8.6
PNG Image Support - Photo images now support read/write in the PNG format, with the ability to set the alpha channel.