On Texas Instruments’ Website, they have a variety of useful, downloadable applications for their calculators — which calculators you can use on the SAT and ACT. You can get a list of area formulas, a Cabri Jr geometry app, a Geomaster geometry app, a conic sections app, a transformations app, an inequalities app, and a polynomial root-finder/systems of equations solver app. Some of these applications might already be installed on your calculator, “straight from the factory.” They also have an application that “provides an easy-to-use interface so you can enter the math problem the same way you see it in your textbook, thereby reinforcing math notation and students’ understanding.”
These are the only applications that would help on the SAT and ACT, I think. But you would need to be able to use the applications quickly — time is of the essence when taking the SAT or ACT. So practice, practice, practice. If you can’t use an app quickly, don’t use it on the test, unless you have gone through a whole math section, done what you could, and have some time left to play.
There is a list of all applications available on their TI-83 and TI-84 applications page.