With worries of big household energy bills this winter, carbon footprint calculators may find a new use as people look for ways to analyse their energy use. "Nos Gestes Climat" (Our Climate Actions, repository) is a piece of software that already does part of this job, and its history shows how an open source project found new purposes addressing some of the most pressing needs of today.

The code itself has already served in at least three very different projects:

• mycompanyinfrance.fr (repository) was originally developed by the French government in 2014 so that individuals and companies could simulate the tax consequences of various situations. The software was greatly expanded in 2018 and was also translated to help foreign companies and non-French-speakers.
• The futur.eco project (repository) forked the code in 2019, reusing the interface and the calculator but removing the code about taxes and adapting it with their own code and visuals about CO2 footprint. The futur.eco site can now simulate the climate impact of many daily purchases and activities as well as automated suggestions for how to reduce the impact of those purchases and activities.

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  Then Datagir and Association Bilan Carbone forked that code and extended it to put all those individual purchases and activities together to give you not only an annual total (screenshot 1) but also a detailed breakdown of which actions and purchases contribute most to your CO2 footprint (screenshot 2) and suggestions, with numbers, for where you might be able to reduce your CO2 footprint (screenshot 3).

It's clear that a lot of the code is still the same. This is a great example of how code released as open source allows others to meet new needs and provide new services with less work. And since the two forks are also open source, improvements can flow back upstream or we could see further forks for new purposes. Maybe a dedicated simulator for household energy consumption, or one for energy consumption of a business.

mycompanyinfrance.fr is already a multilingual site. futur.eco and nosgestesclimat.fr are currently only in French, but if anyone wanted a similar site to exist in a different language, open source gives them two possibilities: The text is all in the repositories, so anyone can translate the strings and submit them for addition, or option two is to fork the project and host their own translated version of either site.

If you know of other interesting similar OSS projects, or if you know about how this code was used in other projects, let us know in the comments section below.