I think you'd be hard-pressed to find a LinkedIn alternative. It's too business-oriented for anyone to care that it's under corporate control. In some sense, that's the whole point.
My understanding of Friendica is that it's supposed to fill a niche similar to Facebook. I've never used it though.
There's definitely more I've accumulated over the past couple years but those two come to mind first. There is also a tool that automates the new community federation process here if your admins participate.
Feel free to reach out in the future if there's anything else I could clear up.