The controls calculator is a tool that lets its users plot root locus nyquist plot time response ie step response impulse response of any transfer function of a control system. Along with various control system plots the app can also convert the representation of any control system from transfer function form to state space form. The controls calculator can also find the roots equations of any degree.
Along with the various control system plots the app also calculates various time domain parameters such as rise time peak time settling time peak overshoot peak undershoot delay time ..etc and it could also determine various frequency domain parameters such as gain margin phase margin gain cross over frequency phase cross over frequency.

The procedure to use the app is very easy just put in the transfer function and select the required plot ie root locus or nyquist plot or time response or state space conversion or roots of polynomial and click on submit to get the result.
The app is free and requires internet connection to sketch the plots.