Steady
This project solved the simple problem of how to convert CSV files into EAD XML. Initially, I would get a CSV file via email and run a script to do the conversion. The library though was written in such a way that made it easy to place a simple web application over top of it. Steady now runs for free with the cloud provider Heroku. Libraries from around the world are regularly using this tool. It has proven to be useful beyond our initial use cases for things like converting legacy container lists into EAD.