Fun, until you want to share an image and have to upload it to a 3rd party, have to explain what a bouncer is to someone who just wants offline messages and AFAIK voice and video chat is not possible.

Client dependent, but channel overview per server is also not that good.

No voice chat.

IRC + Mumble is a good combo in my experience. I only fire up Mumble as-needed since I tend to prefer text chat.

i agree, but you need your people to have 2 logins. Great for friend groups, not working in scale.

Neither one strictly requires a login AFAIK, actually. You can chat with an unregistered nick on IRC, and Mumble has certs, but I think they're optional and don't have associated passwords.