Buttondown, like all software companies, sits on the shoulders of giants. While it is impossible to enumerate every piece of open source technology we rely on, I think it's important to both call out as many as humanly possible and give back in whatever way we can: by committing to donate 10% of all profits to open source technologies that power the software and by open sourcing and stewarding modules that others in the community would find useful.
We — and you, even if you don't know it — would be nowhere without open source software. That's why we're a happy and committed member of FOSS Funders, a group of companies devoted to funding open source software, as well as signatories of the Open Source Pledge.
(Interested in the closed-source software we use? Check out the stack.)
In addition to the below, we also donate $250/year to Adam Johnson, whose projects we use are frankly too granular and numerous to list here, but we are in his debt for all the work he does for the Django ecosystem on our behalf.