What are some alternatives?
When comparing Calligra Plan 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.
Taskjuggler - TaskJuggler is a modern and powerful, Free and Open Source Software project management tool.
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.
FoxPlan - Web-based project collaboration tool
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.