After installing the emulator, it wouldn't run. So I ran Terminal, found the app folder, then found aiStarter. I ran, from Terminal, ./aiStarter, and this is what it told me:
MacBook-Pro:commands-for-Appinventor tomdowad$ ./aiStarter
[621] Error loading Python lib '/var/folders/mx/27frfycj64538crxj2h3lvj40000gn/T/_MEIp7VIii/.Python': dlopen: dlopen(/var/folders/mx/27frfycj64538crxj2h3lvj40000gn/T/_MEIp7VIii/.Python, 10): Symbol not found: _getentropy
Referenced from: /var/folders/mx/27frfycj64538crxj2h3lvj40000gn/T/_MEIp7VIii/.Python (which was built for Mac OS X 10.12)
Expected in: /usr/lib/libSystem.B.dylib
in /var/folders/mx/27frfycj64538crxj2h3lvj40000gn/T/_MEIp7VIii/.Python