The installer has been running approximately 30 minutes and is hung on "Running package scripts...". There's no way to terminate installer from what I can see. I'm on Mac OS Mojave 10.14.1.

6 ways to force quit Mac apps.

Force quitting is what I did. But I couldn't retry the installer because the old one must have left lock files because the installer wouldn't run again. And when I tried to restart the computer, the "fact" that the installer was still "running" stopped me from shutting the computer. Had to use the power button to shut down.

Obviously, this install was never properly tested, and I'm not trying it again. I'm hoping that this aborted install hasn't screwed up my computer.

From the developer:
Charlie Fenton wrote:

The Mac installer can take a long time running its scripts, especially if many user accounts are set up on the computer. Another possibility is that the installer script is waiting for the user to answer one of several questions it may ask. The dialog might be hidden behind another window.

This installer has been run successfully on OS 14.2 by many many users.

If it is truly hung, force quit the Installer app and any PostInstall apps to avoid restarting the Mac.

First I recommend he download a fresh copy in case his original was corrupted. Run the Uninstall BOINC utility provided in the extras folder with the installer before running the installer again.

_Only_ If all else fails, he could create an installer log and post it for me to analyze. As soon as the installer starts, enter command-L followed by command-3. When it has hung, click “save”.