Lots of hackers like to build things relevant to their own hobbies, but the problem is that if you make (say) a WoW character builder, some other hacker will build another one for free. (I don't play WoW so I don't know if my example made any sense, but you can fill in the blank for one that does.) They need to find something non-hackers want.
I don't think there is any list you or 'patio11 has of these things, or else the niche would already be filled. But I think that's what HN'ers want: "tell me what to build!" And they don't know what to build.