Produces this sort of thing:
[][][][][] [][][][][][] [][][][] [][][][] [] [] [][][][][][]
[] [] [] [] [] [] [] [][] [][] []
[] [] [][][][][] [] [] [] [] [] [][] [] [][][][][]
[][][][][] [] [][][][][][] [] [] [] [] []
[] [] [] [] [] [] [] [] [] []
[] [] [][][][][][] [] [] [][][][] [] [] [][][][][][]
Details here: http://org.orgraphone.org/2010/09/the-sinclair-spectrum-font-simulator/
.