Sounds like email.

Problems with email

• Email requires a balance of keeping people in the loop, and flooding their inboxes.
• Requires careful use of cc to keep everyone in the conversation.
• Easy to lose emails - e.g. hermes file limit.
• Easy to miss replies in long email chains.
• Easy to overlook relevant emails from the past.

Slack solves these problems

• Much easier to find conversations that are relevant to you
• Everything is automatically saved.
• The conversation chain is easy to follow.
• Everything is indexed, and a quick search will pick up anything previously mentioned.

• Groups
• Sharing
• Personal messages
• Search