Logisim 2.6.0 allows subcircuit customization

Logisim, a graphical design and simulation tool for logic circuits, is now at version 2.6.0. The headline feature of this new version is the ability to customize how subcircuits are drawn when nested within another circuit. In previous versions, subcircuits would always be drawn as a rectangle with a gray notch at its north end. Users can continue to use this convenient default behavior, but they can alternatively select "Edit Circuit Appearance" and use a drawing interface so that the circuit is drawn in a different way. For example, an arithmetic logic unit (ALU) could be customized so that it appears in its customary V shape.

While customizing subcircuits is by far the biggest feature in this new version, there are some other minor enhancements. Clicking a subcircuit using the poke tool will show a magnifying glass, which you can double-click to enter the state of that subcircuit. And subcircuits can now be rotated after they are placed into a circuit. The Arithmetic library includes a new Bit Adder component which computes the number of 1 bits in its inputs, and the Plexers components can have 5 select bits, allowing for example a 32:1 multiplexer.

Educational institutions around the world use Logisim as an aid to teaching about digital logic and computer architecture. As a Java application, Logisim can run on most major operating systems. Read more about Logisim at http://www.cburch.com/logisim/, and download it from SourceForge.net at http://sourceforge.net/projects/circuit/.