Discourse Platform

Discourse Discussion Platform defines itself as Civilized discussion for your community (see this demo), is a free Open Source platform - as stated on their website:

There is only one version of Discourse – the awesome open source version. There’s no super secret special paid commercial version with better or more complete features. Because Discourse is 100% open source, now and forever, it belongs to you as much as it belongs to us. That’s how community works. Discourse is the discussion platform built for the next decade of the Internet, designed to be used as a mailing list, discussion forum, long-form chat room, and more!

While there is a hosted version of Discourse, this blog explains the details of the process defined in the Set up Discourse in the cloud in under 30 minutes with zero knowledge of Rails or Linux shell. Since that article was written (Sep 14 2017), the actual installation got a lot improved, by DigitalOcean's offering of prebuilt Docker image with Discourse server "baked in":

Image 1 - Select Discourse from the Once-click app tab content

See Droplet creation page for more details - observing that the Discourse server installation implictly begins with the Step 1 - Choose an (Docker) image.