So, I'm building a science and tech forum website and i need recommendations on what features i can add to increase user engagement and returning/active users, basically, recommendations should be something uncommon and unique and from personal preference or experience, thanks :)

Edit: Someone asked for more info on my intended community. Okay, so it's basically going to be a science and tech forum community coded from scratch by us (I'm not using any forum software), we already had it online since last year but it's still on beta version presently, and we currently do not have a good level of engagement/activities from users (i'll blame that on the uncompleted version of our forum community), so we will be finishing up our forum community hopefully ending this month, any ideas on what we can implement on the site to make our tech community stand out from others and be more social and engaging, attracting more users thus growing the community will be very much appreciated.. We do have unique contents i.e tutorials, guides etc

My question: How do we make users: both male and female engaged to our community, our community is focused on science and technology and we plan to have a sub domain where we can blog about science and tech stuffs too i.e blog.example.com...