For sites similar to Hacker News but focused on different topics, you might explore sciurls.com for science, mathurls.com for math, techurls.com for technology, finurls.com for finance, physurls.com for physics, devurls.com for development, hwurls.com for hardware, and tuxurls.com for Linux. These curated link sites are less trafficked, offering a focused alternative to Reddit's vastness.