The free section covers right triangles. Notice it allows you to use the hypotenuse, degrees, base or rise measurements and then it does the rest of the work.
The two sections you must pay for are oblique triangles and circles.
The other two sections are priced at $2.99 each or $5.99 for both and $0.99 to remove the adds. For my students, the only real use I see for it is for them to check their answers, otherwise I don't see using it in my classroom this coming year. The idea is nice but at the moment it is not a real possibly for use in my classroom.