MailClark - The Slack bot for external communications
Talkus - Chat with your website users from Slack
iDoneThis - iDoneThis The fun, easy way to get stuff done. Every day we’ll email your team to ask, “What’d you get done today?” Just reply to our email. The next day, everyone gets an email with the team's accomplishments
Chatlio - When you have a business to run, your average instant messaging software just will not do. You need an internal presence upon which your entire team can collaborate on. Read more about Chatlio.
PigeonBot - Send emails via Slack with the /email command
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.