Chatterino is a Twitch chat client which has a macOS version (along with Windows, Linux, and BSD) that I've been using. It can monitor multiple channels, I think each with a separate login user if you want.

I mostly use it for chat history -- I set it to keep 10k lines per chat which I can then search fairly easily, unlike Twitch UI which only keeps a couple of hundred lines and has no built-in search so you have use browser search. I keep Chatterino running all the time so it can record chats even when I'm not around. Also you can have it log chats to a text file (which I just discovered as I was writing this review) though it loses a bit compared to using the UI to read old chats.

Some nice things:

• Supports various Twitch emote extensions like BetterTTV and 7TV -- I forgot that I also use this since I don't have those extensions installed so I can check what the emote is without looking it up in BetterTTV/7TV.
• You can see deleted messages -- useful where I'm not a mod to see if a user was particularly offensive in another chat in which case I might ban him in the chats I mod.
• Beeps when my name is mentioned. Not sure Twitch does it and I have it off or it doesn't do it at all. A little useful in case someone is trying to get my attention as I'm not always reading chat.
• Can do mod timeouts and bans from Chatterino. But although it has its own notes facility it doesn't integrate with Twitch mod notes so would guess Chatterino notes are for me only. And in general I find Twitch mod view much more useful than trying to mod with Chatterino.

I guess, besides lack of mod tools, the biggest drawback for me is the rather ugly UI.

It's free software. Open Source -- MIT License which looks to be as unrestrictive as BSD License.