Vabotu - More than slack. More than Trello. FREE.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Do - Do helps you run productive meetings. Do work you love.
Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.
Kurator - The premier Chrome extension for savvy researchers and publishers alike. Curate your interest and publish to your website, newsletter and social media sites directly from the browser.
EssentialPIM - EssentialPIM is a free Personal Information Manager that keeps up with the times and lets you manage appointments, tasks, notes, contacts, password entries and email messages across multiple devices and cloud applications.