Crmble - Easy peasy crm for Trello

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

Onesheet CRM - The Simple CRM for Google Sheets

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

SquareOne - Email. Stress-free.

Zendesk Support - Social Customer Support and Help Desk and Ticketing