Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
Salesforce - CRM software solutions and enterprise cloud computing from salesforce.com, the leader in CRM and platform as a service.
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.
HelpScout - Help Scout is a simple, straightforward way to provide excellent support
Padlet - Visual boards for organizing anything.