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
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
Zoho Desk - Industry's first context-aware Helpdesk Software
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
Salesforce Service Cloud - Service Cloud integrates customer service with social networks and provides a self-service customer portal and knowledge base system.
Slack - A messaging app for teams who see through the Earth!