I recently tried out OpenProj and it worked well for some minimal stuff. It seems to be feature rich and useful to open MSProject files as well.
Check it out at http://openproj.org/ or on sourceforge.
OpenProj by Serena Software is a desktop replacement of Microsoft Project. OpenProj has equivalent functionality, a familiar user interface and even opens existing MSProject files. OpenProj is interoperable with Project, with a Gantt Chart and PERT chart.