https://www.designernews.co/ - for designers

http://www.webdesignernews.com/ - for web designers

https://growthhackers.com/welcome - growthhackers

Then of course there's a sleuth of subreddits.... similar to HN would be

https://www.reddit.com/r/startup

If you are looking for something different, there is a tool that lets you create online communities like HN or Reddit, so you can create your own.

http://www.hellobox.co

Quite a few communities on it are

http://www.chitchats.co/ - community to share interesting Slack chatrooms

http://tools.robingood.com/ - curated list of tech tools