For people who don't care for 'apps' that are just websites inside browsers, Slack supports XMPP and IRC gateways. I've only used the IRC gateway, and there are some janky bits, but it got the job done. https://slack.zendesk.com/hc/en-us/articles/201727913-Connec...
The IRC gateway also does not. It typically wasn't an issue for me when I was using it as most of my coworkers at the time did not frequently edit messages.