Our team started this year, and we mainly started with just coaches, mentors, and leads, but during built season we expanded to letting the whole team on. A useful feature if you want to let people on to keep them updated, but don't want them to talk on the channels is on slack, but that's the paid version. The free version is pretty comprehensive though. You can make private channels, direct message, and connect slack to other apps, so it'll interact with google calander, Github, and other useful team organization apps. Our biz team made a podcast in cooperation with other teams on slack and how its being used. here's the link if you're interested.
https://soundcloud.com/frc-team-2415/slack-podcast
It's great though, just had to give a hard push to get the team to use it. We now chat everyday on slack in multiple different channals