Tcl and Tk are distributed under a modified BSD license:
https://www.tcl-lang.org/software/tcltk/license.html

• © 1987-2021 Tcl Core Team and Contributers.
• © 2011-2021 Kevin Walzer/WordTech Communications LLC.
• © 2014-2021 Marc Culler.
• © 2002-2012 Daniel A. Steffen.
• © 2001-2009 Apple Inc.
• © 2001-2002 Jim Ingham & Ian Reid.
• © 1998-2000 Jim Ingham & Ray Johnson.
• © 1998-2000 Scriptics Inc.
• © 1996-1997 Sun Microsystems Inc.