Not that I know much about Slack, but by using GitHub you don't give up control over your repository, or its history. Every single project member has a fully working copy that can be used if GitHub for some reason decides to go rogue, and it's accessible through open source software.
How about your communication in Slack? Can it be withheld or otherwise become inaccessible, or is it completely accessible through open source tools and possible to export continuously to a useful format? If not, then there's quite a difference.
How about your communication in Slack? Can it be withheld or otherwise become inaccessible, or is it completely accessible through open source tools and possible to export continuously to a useful format? If not, then there's quite a difference.