doujin software; hobbyist software
Refers to software, especially video games, created by hobbyist circles (同人サークル) rather than commercial companies. Often distributed at events like Comiket.
He makes doujin software as a hobby.
I bought an interesting doujin software at Comiket.
Compound of 同人 (doujin, 'like-minded people; coterie') and ソフト (sofuto, 'software'). The term emerged from Japanese hobbyist circles producing self-published software, especially games.