Other Microsoft applications, like Excel or Word, can be used in a very general way. That is, you can use a program like Word to compose and format practically anything that you need to present as written work. In Excel, you can build a worksheet to analyze just about any type of information that is suited to a tabular format.
Project, on the other hand, has a more specific focus. This program is designed as a tracking and planning tool for endeavors that involve sub-tasks, multiple resources, and various scheduling goals and priorities. This does not mean that Project lacks versatility. You can use Project to help plan and organize anything from a software development process, to a major construction job, to the expansion of a company.