Korean text is often romanised so that people who don’t read or speak Korean can understand roughly how various Korean words are pronounced. There are various different systems of rules for how to romanise Korean text, and each of these systems has its own special case rules that are difficult to remember.
www.romanisation.net is a simple web app that I created a while ago which can take Korean text, or mixed Korean and English text, and romanise the Korean text according to any of four systems of romanisation for Korean. It implements all of the special rules of romanisation that exist in these systems, so if you need to romanise a lot of Korean text (as I often do), it makes it a lot quicker.
The website itself contains descriptions of the four systems of romanisations that it can use, as well as their special case rules.