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.
UseResponse - Open-source, self-hosted customer feedback software, live chat and helpdesk system that you can install on your server. Organize documentation using knowledge base and get feedback from social networks with centralized system
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
Slack - A messaging app for teams who see through the Earth!