What's the best platform for building an online community?

Give this a try.

Discourse is the best! It's robust and feature-packed that you cannot get away from it. Do give it a try if you have not.

it's great if you have an initial target group of few dozens of people who can be involved there and bring some engagement. it is simple and I know couple of startup, product, fintech retated communities there, which are pretty active

I'd go with Slack as well. I am a member of multiple different teams and most of the are super engaged communities that post and talk interesting stuff daily. Other than that, you could also start a subreddit dedicated specifically to your business or an industry if the business is too niche.

Have you had a look at Telescope? It's a good option if you're looking to take an open-source approach.

Emerging platform from the founder of Ning. It's pretty slick thus far.

Mightybell gave us an easy to use, visually driven community platform that encourages not only engagement but also re-engagement. Highly Recommended!

I've recently found this very attractive and simple tool

I just launched this today and saw your question pop up so I figured I'd share it. Faces is a way to give your _existing_ community an online home. It's not mean for building a community from scratch, but it serves as a nice overview of who's who for example a meetup groups and the like. It strengthens your community by enabling members to easily find each other and connect. Something that's especially tricky for otherwise offline communities.

This is what I use for both the LA Tech community and the Women in Tech community. http://community.wearelatech.com and http://community.womenintech.fm

Depending on what kind of community you want to build, you'll have different needs. But common to most communities are: - communication - scheduling / events - polls That's pretty much what Mobilize has built, plus you don't need to force people to use the web app, which means you get higher engagement. It's free for 100 users, and they've got a cool feature called 'Networks' which means you can scale out the community around certain topics, events or something else. Check it out!

It has tiered levels, can post events, is both on mobile and web, great for ambassadors programs, SMS features plus member only profile directory

I have used it quite a few times and their UI is clean and simple including great functionality.

I would also heartily suggest going beyond the forum if you're trying to create a real community, where there's a greater degree of trust. Video calls are a great way to do that, and Zoom leads the way.

Facebook Live is a pretty cool tool for hosting more interactive versions of what we would once have called 'webinars' or the likes. It's less formal, and has greater reach, which is good if you want to run a fairly open community (or an open portion of it), but obviously not so great if you want to preserve anonymity to your users.

If you're wanting to build a ProductHunt-esque community, check out this WordPress theme which is pretty awesome. It's tracking the features and direction of ProductHunt, so most things PH can do, PlH can do too.

Used this to create my community for IoT developers https://www.iotandus.com.