Logisim-evolution

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!