Tcl/Tk 8.5

Latest Release: Tcl/Tk 8.5.19 (Feb 12, 2016)

The 8.5 release was a long time in development, and brought about several good enhancements to Tcl/Tk.

Features: 8.5 has over 90 TIPs included to provide a wide variety of new features.
Bignums: Tcl now supports arbitrary-precision integers, which improves math operations on large integers.
Safer interps: Tcl's powerful safe interpreter mechanism now has improved control of time and command limits in slave interpreters.
clock command: More robust implementation of command for specifying time, with significant l10n and i18n improvements.
dict command: New data structure that allows access to data by value rather than a variable name, which is substantially faster.
Additional improvements: Faster list search, new and improved mathematics procedures, anonymous procedures, new ways to package Tcl extensions, Tcl-level custom channel types, file and line location information for each command, and more.

New modern theming engine: New and complementary widgets that make use of platform-specific theming on Mac OS X and Windows to better fit in with those environments, and feature an improved look and feel under X11. (screenshots)
New widgets: Part of the themed widget set, Tk now has core notebook, combobox, treeview and progressbar widgets.
text widget: Smooth scrolling, widget peering, and improved procedures for counting and replacing text.
Font rendering: Now uses anti-aliased text under X11, and a more modern text engine (ATSUI) on Mac OS X.
Additional improvements: Window transparency, new fullscreen option for windows, enhancements to specific widgets and window layout, and more.

There is of course much, much more. See 8.5 Changes on the wiki for a complete list of new features.