Another vote for WeeChat an the Slack plugin. Which utilizes the Slack API (so y...

boomboxnation on March 8, 2018 | parent | context | favorite | on: Saying Goodbye to Slack’s IRC and XMPP Gateways

Another vote for WeeChat an the Slack plugin. Which utilizes the Slack API (so you are kind of out on your butt if one of your slack's won't allow you to get a token) Weechat is a bit of work to get it working/looking the way you want, but it's worth it.