An updated version of this keyboard with some missing characters is now available. See this post for details of the improved layout and links to the new files.
Sometimes it is useful to write Sanskrit and other Indic languages in a form that is unambiguous but can be easily read by people who know the Latin alphabet. The standard ways of doing this are with IAST or ISO 15919. The two schemes are almost identical. An example is ताण्डव which can b written as Tāṇḍava. I have produced a windows keyboard that contains the necessary diacritics (accent marks). The normal keys are assigned the same as the standard UK keyboard, only the characters accessed with the AltGr and Shift-AltGr change.
IAST or ISO 15919 indic transliteration keyboard layout (AltGr)
These keyboard driver can be loaded the same way as the bolnagri layout described in the previous article.
The files are located here, with the package zip file and the keyboard creator source file available for download and free use. Though these older files are still available I would recommend that you use the newer package.
IAST or ISO 15919 indic transliteration keyboard layout (Shift-AltGr)
This layout is not based on any other, I have not seen a standard layout for this keyboard. Since this is the first version it means there could be missing characters or usability problems. If you have any suggestions please leave a comment below.
Tandava's Technical Blog 
Thank you, Tandava. I used this keyboard layout on my old computer (with Windows 7) and it was great. I’m having a hard time getting it to work on my new computer though (with Windows 8). Any help would be much appreciated.
After installing the Indic transliteration keyboard, I found some keys interchanged functions. For example, inverted commas ” ” returned @ @ in the typed text and vice versa. After uninstalling the keyboard the keys returned to their normal functions.
It is also not easy to use the keyboard. However, a transliteration keyboard is a very useful tool for scholars. There is another transliteration keyboard available but it does not have all the diacritics of Indic languages.