You could harden a Linux server by killing the init process. That would cause a kernel panic, and prevent new processes running (e.g. shells). Existing processes like Web servers would continue to function, so you could put this at the end of the boot script :)

I never thought that is possible! Kind of stupidily funny and brilliant at the same time.

Or, how to specify different git config (name, email, sign key) for projects under different directories.