ReadNotify - ReadNotify enables the user to know when email is sent and the reciever reads the email.

Freshdesk - Freshdesk is a cloud-based customer support software that lets you support customers through traditional channels like phone and email, social channels like Facebook and Twitter, and your own branded community

Bananatag - Find out what happens to your emails after you press send! Add email tracking, attachment tracking, email scheduling and templates to your daily emails.

Salesforce Service Cloud - Service Cloud integrates customer service with social networks and provides a self-service customer portal and knowledge base system.

GetNotify - GetNotify is a free email tracking software solution.

Zendesk Support - Social Customer Support and Help Desk and Ticketing