Utility and applicability of astronomy, physics or mathematics is a subject appropriate for an extensive and serious article with philosophical implications - the mere statement that each of these disciplines has different applications is just a commonplace. Every research in science contains the implicit question :"What's the use?", even if the ultimate aim is just to satisfy human curiosity.

Many applications are obvious and intended. There are, however, those that are unexpected and unplanned. It sometimes happens that research results turn out to be useful in some surprising way; sometimes the research itself may benefit from unforeseen instruments imported from other domains.

We feature such situations in this issue of WWW Delta. All the texts are intended to exemplify this very broad area, which we decided to call non-typical applications. We wanted the panorama presented here to be like a view from a high Alpine peak on a sunny October morning: you can't see the entire world, the details are dimmed, but still the view is surprisingly vast and varied - and maybe the blue shapes seen on the horizon will become the destination of future excursions for many a reader.