From Mike Witcombe:
ProjeX is an Excel add-in that replaces some of the functionality of Microsoft Project when tracking projects using Gantt charts. The user does not need to spend hundreds of dollars on a piece of complex software when ProjeX can quickly and simply track progress using Gantt charts and Excels standard functionality.
As an Excel add-in ProjeX requires very little extra disk space (unlike Microsoft Project) and does not require the user to learn yet another software package. All Gantt sheets are generated from Excel sheets and produced as either Excel sheets or charts. This gives the user all the power and flexibility of Excel without the training overheads of battling with Project