Stallman's seminal contribution, to my mind, transcended the coding, as central as that was -- it was in articulating the vision of a free operating system, providing the first roadmap, hacking copyright to keep such a system free, and organizing and inspiring others to join him in making it happen. Those who were not involved with computers in the 1980s are unaware of the centrality of Stallman as a figure then. Only in the late 90s did well-organized corporate opposition to the FSF emerge, resulting in the creation of the pathetic shill-central of the "Open Source Institute", the elevation of minor fringe figures like ESR into (for a while at least), wise prophets, and the calculated exclusion of Stallman from visible speaking roles at most industry conferences, and organized campaigns of vilification and character assassination against him.
I regard the code I've produced within my subdiscipline as an extension of
the GNU project since 1984. I know that even in the BSD framework, the freeing of that code and its general availability in fully free distributions is in large part a legacy of GNU's advocacy -- and more importantly -- example. Much code has been freed simply to stay relevant in an era where the philosophical firmament was set by GNU.