The original operating system for the Apple [L1 ] Macintosh Computer (which was not the first computer from Apple - it was actually a fourth or more generation computer). Also called MacOS Classic to differentiate from MacOS X.
These days, most Macs are coming with MacOS X installed.
Note that Daniel Steffen and others provide Tcl, Tk, and even Tclkit in formats suitable for MacOS Classic (both 68k and Power PC!), up to Tcl/Tk release 8.4.2.
However, support for the MacOS Classic platform was dropped from Tcl/Tk as of version 8.5.
DKF vaguely remembers the Apple ][, which is kind-of awkward to type in the Wiki... LV has several models of these still - though that is likely to change in the upcoming weeks.
See QuickTimeTcl as one of the Mac specific extensions.
The archive for the main MacOS Tcl mailing list appears at http://sourceforge.net/mailarchive/forum.php?forum=tcl-mac
Daniel announces release of MacOS X 8.4.5 binaries [L2 ] of his TclTkAquaBI distribution. Note particularly the list of all the neat extensions he builds in (or doesn't, depending on which flavor of his binary you choose).