Logisim is an educational tool for designing and simulating digital
logic circuits.

Features:

* It is free! (Logisim is open-source (GPL).)

* It runs on any machine supporting Java 1.4 or later; special
  versions are released for MacOS X and Windows. The cross-platform
  nature is important for students who have a variety of home/dorm
  computer systems.

* The drawing interface is based on an intuitive toolbar. Color-coded
  wires aid in simulating and debugging a circuit.

* The wiring tool draws horizontal and vertical wires, automatically
  connecting to components and to other wires. It's very easy to draw
  circuits!

* Completed circuits can be saved into a file, exported to a GIF file,
  or printed on a printer.

* Circuit layouts can be used as "subcircuits" of other circuits,
  allowing for hierarchical circuit design.

* Included circuit components include inputs and outputs, gates,
  multiplexers, arithmetic circuits, flip-flops, and RAM memory.

* The included "combinational analysis" module allows for conversion
  between circuits, truth tables, and Boolean expressions.

NOTE: The development of this project is suspended. See:
http://www.cburch.com/logisim/retire-note.html