HEY - Email at its best, new from Basecamp.
Mailtrack.io - The best email tracking solution I've found. Free
InstAddr - Disposable email address application.
Saleshandy - Saleshandy is a cold email outreach platform that enables marketing and sales teams to scale their email outreach operations seamlessly.
Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
Gmelius - Gmelius is the first collaboration platform designed for G Suite and your company's daily tools.