My idea of for fun is to release something people will use. I have more fun if I work on something useful. For me is less the journey than the end goal.

I love working on software, architecture, design but only if I see some use.

Of course, for other people, the journey is more interesting than the destination and they have fun hacking stuff just for the sake of it. They discover things and learn new stuff they wouldn't have learned otherwise. And this is a path at least as valid as the other.