Discord is free, you don't need to setup a server, and it can be run from the browser or an .exe or even as a phone app. It also has a far more robust chat system than Facebook too.
I was super stubborn about it for ages thinking "I already have Ventrilo, Mumble, Teamspeak and Skype for the different groups I'm in - why do I need another one?" honestly since switching to Discord I haven't looked back.
I can honestly liken it to when I made the jump from ICQ to MSN Messenger back in the back day, Vent/TS/Mumble just seem ancient in comparison now. Much like ICQ seemed cumbersome compared to MSN back in the day.