MPP and other similar files are Project file formats that are created by Project Management software such as Microsoft Project. A project file is a collection of tasks, resources, and their scheduling to get a measurable output in the form or a product or a service. Gantt charts are used to establish a visual flow of activities against time for the identified tasks that can also be exported to PDF or image formats for documentation. Primavera P6 is another Project Management Software by Oracle that provides complete project planning.
Learn more about Project Management File Formats
The complete list of apps that are split by category to open and view files online.