Hi! First of all, QEMU rocks! I'm from the IncludeOS project, and QEMU is, without a doubt, one of our favourite tools! (If you haven't heard about IncludeOS, it is an open source unikernel operating system written in modern C++ (you can find out more about the project at http://includeos.org/ and https://github.com/hioa-cs/IncludeOS or see a very well received presentation at https://www.youtube.com/watch?v=t4etEwG2_LY from this year's CppCon).
One of the demo applications for IncludeOS is Acorn, a self-contained web server that includes its own OS, can serve static content, handle REST requests and provide an interactive real-time dashboard. The source is available at https://github.com/includeos/acorn and there is a live preview running at http://acorn2.unofficial.includeos.io/ We frequently distribute Acorn demos as QEMU images, and we thought that maybe this could be a candidate for inclusion in your advent calendar? Let me know if this is of interest to you or if you need further information! Ingve