Cool, really enjoyable to play around with. This made me notice a cute (probably trivial) phenomenon that I haven't seen before. If you take x^n+...+1 and move one of the roots to 1 (equivalently, divide x^(n+1)-1 by (x-z) where z is some nth root of unity), then the resulting polynomial's coefficients seem to be the nth roots of unity.
By the way, it doesn't seem to prevent you from entering a degree higher than 7 if you enter the number manually even though it gives off a warning. Not sure if this is intentional.
I wanted to keep the UI from getting too busy, which is why I limited the degree to 7. But if somebody really wants to play with higher-degree polynomials, I'm not going to stop them!
By the way, it doesn't seem to prevent you from entering a degree higher than 7 if you enter the number manually even though it gives off a warning. Not sure if this is intentional.