Logisim is described as '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' and is a circuit simulator in the education & reference category. There are more than 10 alternatives to Logisim for a variety of platforms, including Windows, Linux, Mac, Web-based and Self-Hosted apps. The best Logisim alternative is Digital, which is both free and Open Source. Other great apps like Logisim are Flowgorithm, BOOLR, Hradla and Logisim Evolution.
The project has been picked up again, and has great support for packing subcircuits into the same file. Interface feels outdated, but overall it has an excellent number of features.