"Project management is like juggling three balls - time, cost and quality. Program management is like a troupe of circus performers standing in a circle, each juggling-three balls and swapping balls from time to time." - G. Reiss
As with so many things in life the use of technology can either make things so much simpler, or that much more complicated. Project management in and of itself is a multi-faceted, intricate process that doesn't need any further difficulties. As such the central idea behind project management software is to facilitate the operation.
Common attributes of Project Management Software
Techopedia provides a good list of the primary functions of project management software:
Of course each function is far more complex than just the examples listed here and TechSoup provides a more in-depth look at each component.