To me Slack is just one of those "ooo lookie, corporate option!" kinda products. The kind of product middle managers and hack tech leads pitch to higher ups b/c it makes them look 'relevant' and 'with it'.
You can easily run an XMPP server and take care of your 'company-wide communication' issue, but that requires work and know-how.
Cybrespace is an instance of Mastodon, a social network based on open web protocols and free, open-source software. It is decentralized like e-mail.