Plan for Windows

Plan is a project planner which is similar to, and compatible with, Microsoft Project.

Plan for Windows can be used in various ways:

As a viewer for Microsoft Project files - it can directly read and write Microsoft Project files (MPP/MPD/MPX can be read, MPD/MPX can be written).
As an inexpensive alternative to Microsoft Project. Plan doesn't have all the bells and whistles of Microsoft Project, but this makes it much easier to use.