Slack is a team communication tool. That means it has slightly more robust features than a simple chat app, like threading conversations or channels for specific topics.

Slack is not Open Source and it is not end-to-end encrypted.

It was acquired by Salesforce, who have been gradually reducing free options as it orients it towards enterprise companies.

Admins of a Slack could hypothetically read private messages between members of the Slack.

Free Slack now has a 90 day limit on access to messages and their history, requiring you to pay for a paid account to access them. This puts you on a per user tariff, which can be expensive for large community groups.

Fortunately, there are similar apps like Element, Mattermost, Rocket.chat and Revolt.