Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.

Trello for Slack - Organize anything with anyone, inside Slack

Zendesk - Zendesk is a beautiful, lightweight help-desk solution.

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

Halp - Slack-first ticketing for internal helpdesk

tawk.to - tawk.to is a free live chat app that lets you monitor and chat with visitors on your website or from a free customizable page