I've decided to release a very preliminary version of the Joomla Component I am developing. It provides a GUI front end to nmerge. The point of development it has reached is that it has a single view, an import page and a list of available MVDs. It hasn't been extensively debugged but I just want to get something up there so people can see that it is being developed and if they really want they can try it out, warts and all, and as incomplete as it is. As soon as I can I'll post a new project on Googlecode and provide a link to it from here. You can already see it in action on the Harpur Site. For the record, here are some screen-dumps of single-view with the windowbox facility.
Windowbox, when expanded, updates automatically as you scroll. You can also find the variants of any passage by selecting it. In order to do that it embeds invisible markers in the text which are used to tell nmerge where the selection begins and ends. These markers have a resolution of 256 bytes, so precise variation is not obtainable by this method. Further improvement is possible, but it is hard to derive the exact selection of the original text from the HTML version of it, and to do that consistently across platforms.
Single View with collapsed Windowbox
Single View with expanded Windowbox