At first glance Slack seems to be completely free, but its not.
A free option is available with some limitations that might be noticeable after a few months of usage.
The rest are paid plans and there are three of them: Pro, Business+, and Enterprise Grid.

The more money youre willing to spend, the more features youll get from Slack.
The greatest benefit of making a Slack team is that you and your associates can work more efficiently.
Tasks can be assigned more quickly.

Slack has plenty of configuration options.
Emojis can be customized.
Spellcheck can be disabled if you dont need it.
There are options to customize the notifications too.
By default, Slack notifies you every time an associate sends you a message.
it’s possible for you to pause all notifications and only receive them during a certain period of time.
There are several kinds of notifications.
you’re able to change the sound for each of them.
A preview of the message is shown in each notification, unless you choose to disable it.
The notifications can be delivered via either the Windows Action Center or Slacks built-in notification.
Slacks functionality is expandable by adding apps.
Its not just cloud storage.
There are plenty of other apps.
With everything it has, it is unsurprising that many users like Slack.