Chanty
Chanty (https://www.chanty.com/) is a team communication and collaboration software that helps businesses establish communication via instant messaging and voice or video calls. Administrators can create messaging channels, add or delete members, archive conversations, and assign administrative roles to multiple users. I believe it is better than Slack. As a free alternative to Slack with no message history limit you still get access to most of Chanty features. The paid plans are twice more affordable compared to Slack chat as well.