A generic comment: since wpForo seems to do everything within the script (because of the way it is designed, caching, seo, social), be careful not to over do it and produce a memory and resources hungry plugin.

Okay, so I have WordPress Social Login 2.3.3 installed and running well, which I think goes towards the original point of this thread. What I was thinking though was of a way to have an option at registration, and any other time the user wants, to send an invite to all their Facebook friends to join the forum.

I've done an exhaustive search for plugins, but most seem to be last updated 2 or 3 years ago. Does anyone have any idea whether this is possible or is something that has been shut down through closing off APIs?

And if no longer an option for Facebook, what other social media platforms will allow this and what plugins are there for those? I'm currently allowing people to access the forums with Facebook, Google, Twitter, Goodreads.

BTW, I've checked Facebook API and added Facebook Login button on Registration and Login page of wpForo. This is the first step of wpForo - Facebook integration, we'll do our best to make wpForo social network friendly in future releases. All changes are debugged and optimized, those don't affect wpForo speed and server resource usage.