This app lets you view mpp files without the need to install MS Project.
It is a fast and light weight service that reads the native .mpp file format and does not require any previous installation of Microsoft Project on the user's computer.
Viewer for Microsoft Project, Open and Print MPP files, You can convert a MPP, MPT, Microsoft MPX, XML, or Minitab MPX file to PDF format.

Compatible with Microsoft Project 98, 2000, 2002, 2003, 2007, 2010, 2013, and more.
Provides connect with Google Drive™. You can open a MPP, MPT, MPX, XML file from Google Drive™.
You can open a MPP file to view from your computer or your Google Drive™.

The app also provides the ability to convert project plans from various file formats to XML (MSPDI XML) format.
ex) mpx, mpp, mspdi, mpd, planner, primavera p6/p3, primavera suretrak, powerproject, phoenix, fasttrack, ganttproject, turboproject, sdef, and more.