What are some alternatives?
When comparing GNOME Planner and Microsoft Project, you can also consider the following products
GanttProject - Project scheduling and management tool
Asana - Asana project management is an effort to re-imagine how we work together, through modern productivity software. Fast and versatile, Asana helps individuals and groups get more done.
LibrePlan - LibrePlan is an open source web application for project planning, monitoring and control.
Wrike - Wrike is a flexible, scalable, and easy-to-use collaborative work management software that helps high-performance teams organize and accomplish their work. Try it now.
Basecamp - A simple and elegant project management system.
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.