A non-esoteric answer: in Forth dot prints the top of the stack and function calls are separated by spaces. Hence three dots separated by spaces is the simple and straightforward way to print the top three stack elements.

It's valid in PowerShell, if "." is defined as a function:

  PS> function . {$Args}
  PS> . . .
  .

The first dot is an operator which invokes a command in the current scope, the second dot is our command ".", and the third dot is passed to the command as a string.

It works (almost) in Scala:

   def `. . .` = println("That's valid syntax!")
   
   @main def entryPoint = `. . .`

[ https://scastie.scala-lang.org/BsvbSctXTmaGWaCbM6JX9Q ]

I said almost because HN suppresses the back-ticks…

You can write a function in Bash like this:

  .(){ :; }

This creates a function called "." that does nothing.

Then this is valid code:

  . . .

Befunge