My 7yo son has been interested in boolean logic. I thought surely something like this exists where I can show him how you can chain gates to build larger systems. Couldn't find one! Will have to download this tonight.
Logisim is a nice FOSS software in this space as well. I've designed a CPU in it during COVID, which then became a never-finished breadboard project that stilll looks at me accusingly from some corner of my living room. Oh well.
In addition to boolean logic, Logisim also includes more advanced components such as static RAM, as well as interesting things to drive with it, such as displays. It was developed for use in schools and is therefore designed to be easy to work (or rather play) with.
The project itself has been dead since 2011 or so, but there is an actively maintained fork [1].