There's a new free open source forum software called FOREM software that I came across while browsing another webmaster forum. From a member standpoint, it gives me social media vibes specifically Facebook vibes. According to the developers, it's a difficult software to set up properly, so if you're up for a challenge and want to try it out here's their link. There is a waiting list for those wanting to sign up for their cloud hosting services instead of self hosting, though I'm not sure when this will launch.
[Forem] Community for Everyone
The reason you joined the Internet. Forem provides open-source tools to help you host a thriving, focused, and adaptable community.
www.forem.com