Topic: Feature Suggestion
I think a useful feature would be more automated "Insert function" features like how you can insert a function's derivative function automatically. For example, an option to insert f''(x) or higher derivatives, without having to make the first derivative function first and then take it again.
Another example would be to automatically insert a Taylor series by choosing a function, the order of the series, and the point to center the series on. Finding the curvature of a function is another example.
Perhaps users could even enter their own custom automated functions, similarly to the way you can insert custom trendlines. For example, you could automate inserting the curvature function of a function by creating an option that takes an existing function and creates a new function:
This feature would be useful for automatically inserting things like involutes for parametric functions, or arclength functions (using the numerical integration feature).