Vabotu - More than slack. More than Trello. FREE.
Focuster - Ditch your todo list for an intelligent scheduler
Attentiv - Simple collaboration with upvotes, polls and anonymity
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.
Taskbook - Like Trello but for the Terminal