Tech Crunch has this article about how FB and presumably all of the non-specific topic sites don't have the same feel and aren't generally as good for communicating or community building.
dev.to is the best new private community for software developers and it came to my mind first while reading this article. I never could get into the discussions or over the poor UI of the phpBB forums of which the author writes. It was just too much.
Thanks dev.to for being the best new topic site and filling a much needed hole.