The "National Library at Kolkata romanisation"  is one of the most widely used transliteration schemes in dictionaries and grammars of Indo-Aryan languages and Dravidian languages including Malayalam.
The "National Library at Kolkata romanization" scheme is a popular method for transcribing sounds from Indo-Aryan and Dravidian languages, such as those found in dictionaries and grammar books. It's particularly common when dealing with Malayalam.