Limon Font Keyboard ((link)) -

Double-click the font file and click Install Font in the Font Book application.

Unlike modern Khmer Unicode, where you type based on phonetics, Limon is a "legacy" font. This means the computer thinks you are typing in English, but the font displays Khmer characters instead. The Mapping Logic limon font keyboard

(Note: Shift keys often produce the second form of the consonant or vowel, or a different vowel entirely. This layout is not intuitive for beginners.) Double-click the font file and click Install Font