Note: Monotize is now part of Type – a toolset for working with text in After Effects.
Monotize is an After Effects script that lets you make any text monospaced (regardless of font).
The script is straightforward to use. Select a text layer, then click the add monospacing button.
But, you can also add variable spacers by holding shift while you click to give yourself more control over the spacing of each character in your text.