Autochartist offers an awesome "Chart Pattern recognition" system. They needed a bridge/api between their web service based product and the MetaTrader 4 platform. One of the challenge was that we were asked to do this natively in mql4 and to not use any dll's. So we wrote a pretty slick xml parser in mql4 then created some wrappers for the autochartist web service api.
From past experience we also added the ability to drag and drop the display any where on the charts.