Shiny is a web application framework for R. The idea is simple: deploy R code in webpages. This might prove useful when user interaction is required, for instance to design and deploy forecasting experiments that need human participants.
I gave it a try to see how easy is it to build a demo. Assuming your R skills are ok, then using shiny should be straightforward. It took me a couple of hours starting from zero to get a somewhat complex example for forecasting using MAPA, for which there is already an R package.
Update 11/04/2014: I have revisited the code for the MAPA demonstration. The new one can fit within the normal blog page, but if you prefer the full screen version you can still find it here. You can also still find the two necessary files for the old version of this example, one for the server running the R code and one for the user interface.