This looks difficult to install. I can see there's a core command line module and a GUI in different projects. I don't see a homebrew incantation or macOS installer or anything like that. Looks like python dependency hell.
To someone with no money to spend, Mathematica isnt really an alternative to Mathics.
pip3 install Mathics-omnibus
levels of hard. I'm missing some libraries on one of my machines, but I'm planning on playing with it.