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
Slacking Pigeons - Chat in real time with your users directly from Slack
PigeonBot - Send emails via Slack with the /email command
Avochato - Text messaging for your business.