When you sign up to Planbox, your first organization automatically gets a 15 day free trial which allows unlimited collaborators.

No credit card is required during the trial period. When the trial ends, the organization has to sign up to a paid plan. If the organization does not subscribe to a paid plan, its initiatives and projects will become read-only.

Please refer to https://www.planbox.com/pricing/ for the latest 
available plans and features.