If you need a light-weight Microsoft Project clone, or simply a MS Project viewer, here are a couple solutions :
- OpenProj : http://openproj.org
- GanttProject : http://www.ganttproject.biz
Both can open MS Project .mpp files, so both can do a reasonable job if that's all you want to do. If you want to actually set up a project, OpenProj seems to be the more capable. GanttProject also seems to lack horizontal scroll bars, so I couldn't navigate the timeline well. It also doesn't seem to import predecessors and durations from .mpp files, so again the nod is to OpenProj.
But OpenProj's "Common Public Attribution License" seems to be more restrictive than GanntProject's GPL license. See respective license for details.