Hacker News is basically a list of problems that need solving, or startups/libraries/repos/products that are trying to solve a problem. World hunger is probably one of the biggest problems, so frankly this should be pinned to the top of the home page until somebody finds a way to solve it ;)
It's actually not a list of problems but list of technological tries to solve a problem, thus it has a 'hacker' in the name. There is nearly infinite amount of problems all around the world of various levels of importance, shall they be reported and pinned here as well, like climate stuff, food/water pollution, health, etc. "untill somebody finds a way to solve it"?
"On-Topic: Anything that good hackers would find interesting. That includes more than hacking and startups. If you had to reduce it to a sentence, the answer might be: anything that gratifies one's intellectual curiosity."
