We have developed a Khmer keyboard for Unicode Fonts, copying as much as possible the ABC and Limon keyboards, in order to reduce when possible the necessary re-training to change from using legacy fonts to use Unicode Fonts. The keyboard also takes into account the frequency that each letter is used in Khmer. The layout of the keyboard can be found in PDF document.
We have both Windows and Linux drivers for this keyboard (thanks to Jens Herden):
The Windows driver can be installed in Windows 2000 and Windows XP (Khmer Unicode fonts do not work in Windows 95/98/Millenium).
First you have to decompress the downloaded file. In order to install the Khmer Unicode Keyboard Driver use the Windows Explorer. Right click on the file KhmerKbd.msi offers a menu entry 'install'. Choosing this entry will install the driver and display a success message.
Once installed, you need to go to Start-->Settings-->Control Panel and open the Regional and Language Settings control panel. In there, you must select the Languages tab and click on Details. Click then on Add and select Catalan language (there is no Khmer, and the sign for Catalan is CA, which we can be consider to mean "Cambodian"). Right under, in the Keyboard Layout/IME box, select "Khmer Unicode Keyboard (NIDA 1.0)". Click on OK as many times as needed to get out of the control panel... and you are ready. On the lower right part of your screen you will have the initials for your normal language (EN if you work in English), if you click there you will be able to change to Catalan (CA), which will turn your keyboard into a Khmer keyboard (Shift Alt also works).
The layout of the keyboard is in the PDF file that comes with the compressed driver.
The Linux XKB driver comes together with the instruction to make it work. XKB format is not specially well prepared to render characters that require more than one Unicode character, so installation is not straight forward, but all the instructions are in the README file that you will find in the package.
The PDF with the keyboard layout is also in the package.
The NiDA Khmer keyboard layout for Macintosh was designed by Andrew Carson using Ukelele (a free program available from SIL).
Andrew has also designed a second Macintosh keyboard for writing Ratanakiri minority languages using Khmer script. As in these languages words are separated by spaces, the ZWSP in the spacebar has been replaced by a normal space (as in English). In this keyboard OPT+Space produces an EM-SPACE (U+2001, a shorter space).
In both keyboards, if the caps lock is depressed, the output will be as a standard English keyboard.
To install these keyboards, copy the two files to /Library/Keyboard layouts, then select from the International pane in System Preferences (if they do not appear there, log out and then in again).