Logisim-evolution is a completely free and open-source educational, cross-platform software for designing and simulating digital logic circuits.

Project highlights:

• easy to use circuit designer
• logic circuit simulations
• chronogram (to see the evolution of signals in your circuit)
• electronic board integration - schematics can now be simulated on real hardware
• VHDL components (components whose behavior is specified in VHDL!)
• TCL/TK console (interfaces between the circuit and the user)
• huge library of components (LEDs, TTLs, switches, SoCs)
• Supports multiple languages
• and more!