Apple - Can I run top as screensaver?

If you're looking for hackerish screensavers, the old Xscreensaver bundle was converted to OSX a while ago.

Nicely hacker type examples would be Sonar, AppleII, and Phosphor. Possible GLMatrix too.

However, to answer your question: https://superuser.com/questions/420546/osx-run-bash-or-app-as-the-screensaver

Write an applescript to run Terminal, run Top, and fullscreen itself. Then put that script into the app.

If you install the OS X version of XScreenSaver, the phosphor saver simulates an old phosphorous terminal display. It can be configured to run any command in the terminal display, including top:

I find the settings -scale 2 -delay 40 -program top work quite well, and look quite "hackerish".