A simple command line REPL (run it with a headless image)

repl.st

OSProcess thisOSProcess stdOut 
  nextPutAll: 'Welcome to the simple Smalltalk REPL'; 
  nextPut: Character lf; nextPut: $>; flush.
[ |input|
  [ input := OSProcess readFromStdIn.
    input size > 0 ifTrue: [
      OSProcess thisOSProcess stdOut 
        nextPutAll: ((Compiler evaluate: input) asString; 
        nextPut: Character lf; nextPut: $>; flush 
    ]
  ] repeat.
]forkAt: (Processor userBackgroundPriority)