I've been working on a project for Orbiter using Google Apps Script. In that environment you use Javascript for both the client and server.
Basicly, the app is a replacement for the excel sheets I've been using over the years to plan flights in Orbiter, with special focus on the use XR type vessels and cargo missions. I wanted to calculate various aspects of the flight in very high detail without the need to do any copying and pasting in text files.
I've created a wrapper around the NASA trajectory browser which scrapes all the hidden good stuff and then transforms it into a flight plan which can be edited. It allows to select cargo containers, runs the rocket equation after each change to calculate the needed main and APU fuel, LOX and any external fuel containers if neccesary. Also, it automatically sets up the MFD's depending on the phase of the flight so you don't have to set these up each time you load a scenario. The cargo is loaded in a logical order, so the empty main fuel containers which are to be deployed first are sitting on top of the regular cargo containers.
When finished setting up the flight, it offers a download for an archive in the typical Orbiter add-on structure, so these files are to be unzipped in the main Orbiter folder. It contains the scenario file, the xrcfg file and more.
The app is not finished, but I will see if I can make it available for other users to have a look.