Flock is a communication-focused Slack alternative
Flock is another application very similar to Slack but is arguably a little less daunting to use and offers more comprehensive communication tools.
There’s also integrations with third party applications like Google Drive and Twitter, with notifications appearing directly in channels.
Flock is free to use, but searches are limited to 10,000 messages, there is a 5GB storage limit and only five third party integrations are permitted. A Pro plan adds unlimited search, 10GB of storage per user, and admin controls, while the Enterprise plan ads 20GB of storage per user, more admin controls and dedicated support.