I created a tool to take project plans from a tool that we use to model schedules and generate gantt diagrams from the data in a way that is better than the commercial tool. It's all just a zip file containing an html file and a couple of javascript files. Others in our company are using it now as it is easier and produces better output than the modeling tool.

When I decided on a local html for the app, I wanted something that did not require installing a language like python, did not require installing, and would work on Windows and Mac.