All of them? I do wonder if anything I have ever worked on has actually been useful in a real, honest sense. Yes, people use stuff I've worked on or been a part of and possibly still even do (and there's plenty of stuff that wasn't used at all or canceled similar to your story), but it's hard to know the projects' actual usefulness. Perhaps it depends on the definition of useful. I'd say that if something makes someone or something safer, happier, healthier, or some other similar criteria, then that was useful. But I'm not sure I've worked on anything like that, and I'm not sure most people do either.