TkGate is a digital circuit editor and simulator with a Tcl/Tk based
interface.  TkGate includes a large number of built-in devices
including basic gates, memories, ttys and modules for hierarchical
design.  The simulator can be controlled either interactively or
through a simulation script.  Memory contents can be loaded from
files, and a microcode/macrocode compiler (gmac) is included to create
tkgate memory files from a high-level description.  The simulator
supports continous simulation, single step simulation (by clock or
epoch) and breakpoints.  Save files are in a Verilog-like format.

TkGate also includes a number of tutorial and example circuits which
can be loaded through the "Help" menu.  The examples range from a
simple gate-level 3-bit adder to a 16-bit CPU programmed to play the
"Animals" game.

For more information on TkGate, see the TkGate web site at:

WWW: http://www.cs.cmu.edu/~hansen/tkgate/

Program and FreeBSD port by: 
  Jeffery Hansen <hansen@cmu.edu>
  http://www.cs.cmu.edu/~hansen