@kaha : See here:
A minor note: the software this site supports are not simply freeware – they are not only ‘free as in beer’, but ‘free as in speech’ (libre / free and open source software, FOSS). People don’t just get permission to use them for free, but are also allowed to study them, take them apart, build modifications (of course not everyone has to do that), and publish those. For the average user this means that the developers of darktable (or any other tool here) can’t simply decide one day they go shareware or commercial, or simply stop developing, without giving others the chance and right to continue if they are interested.