Access
Microsoft Access is a desktop database tool. Access is a great program and is as underrated as it is overlooked by most people. You can create your own desktop database applications. An example of a database application would be an inventory tracking system where you have forms that allow you to read or edit the information you need, and data tables to store them. Where Excel has worksheets, Access has tables. And where Excel has formulas and functions, Access has a graphical SQL query generator where users can simply point and click to create powerful queries without having to learn SQL.
Outside of true modeling and analysis, most people over-use Excel where Access would be the better choice. Learning this program will launch your productivity to the next level, even if you only learn the basics.