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.
This is something you mom tells you the first time you buy avocados as a child. Wrap them in newspaper to ripen faster. Keep away from bananas to last longer. It's definitely not something that "gratifies one's intellectual curiosity".
What to Submit
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.