https://discordapp.com/

All-in-one voice and text chat for gamers that’s free, secure, and works on both your desktop and phone. Stop paying for TeamSpeak servers and hassling with Skype. Simplify your life.
You'll never go back.
It's free and pretty rad.

It's like IRC/Slack mixed with Skype/Teamspeak. Could be good for coordinating or chatting with other FC members. It's definitely more focused towards PC gaming although I've used it to chat w/ my buddy while playing through Halo 5 CoOp. It also features Twitch.TV integration which is a pretty nifty feature if you want to build your community outside of the ridiculous twitch chat.

I created one here if anyone wants to check it out!