I started using Slack some time ago and much prefer it over email and chat apps such as irc. Slack is described as A Messaging App for Teams but I find that team does not have to be limited to professional associations can include personal groups as well. I am currently a member of a long-lived email list (more than 20 years) that used to be very informative but now regularly degenerates into discussions that include 15 or more replies in a thread. Slack makes it easier to follow a discussion and is archived so that new members will see previous posts related to a subject. Slack provides the ability to create topic specific channels which prevents a single channel from becoming muddled with numerous discussions.

A friend described Slack as just being irc with a new UI but I disagree with that assessment. I think that Slack is more modern and supports a number of facilities that enhance it (bots, and and API) that are also supported by IRC but I find it easier to both use and integrate with I have found that the Slack OSX app is not as reliable as I would like. It does seem to crash once every couple of days but the advantages outweigh any issues that I have experienced to date.

If you have not tried Slack I strongly recommend it.