Logisim is an educational tool for designing and simulating digital logic
circuits. With its simple toolbar interface and simulation of circuits as
you build them, it is simple enough to facilitate learning the most basic
concepts related to logic circuits. With the capacity to build larger circuits
from smaller subcircuits, and to draw bundles of wires with a single mouse
drag, Logisim can be used (and is used) to design and simulate entire CPUs for
educational purposes.

Logisim is used by students at colleges and universities around the world in
many types of classes, ranging from a brief unit on logic in general-education
computer science surveys, to computer organization courses, to full-semester
courses on computer architecture.