An alternative to Zulip is Twist - https://twistapp.com. (I'm not affiliated with them at all; just a fan.)
They have a proper native (as in not Electron-based) Mac OS X app (probably other platforms, too, but I haven't checked), which launches almost instantly and consumes a very reasonable amount of RAM. It's definitely worth a look.
They have a proper native (as in not Electron-based) Mac OS X app (probably other platforms, too, but I haven't checked), which launches almost instantly and consumes a very reasonable amount of RAM. It's definitely worth a look.