I can hardly imagine a software project where the things to do are not somehow collected in a formal/informal document, be it a SRS or a simple note. So I was searching for these requirements documents for some well-known Open Source applications (e.g. Signal, GIMP, VLC, ...). As the Source is open, I guess engineering documentations can be as well, be it according to Waterfall, Agile or other methodologies. But I have not found any. So where are requirements captured for open source projects?