Bowde
A browser-based control-systems workbench: type a transfer function and watch Bode, Nyquist, Nichols, pole-zero and time-response diagrams redraw together as you sweep its parameters.
Overview
Desmos, but for transfer functions
In MPSI preparatory classes I leaned on Bode and time-response diagrams to understand how a dynamic system actually behaves, and then to tune it. Outside professional software like MATLAB there was nothing lightweight that could draw those diagrams from a transfer function and keep them live while you changed it. Bowde exists to be the free, instant, browser-based version of that loop.
It borrows the model of a graphing calculator: you type G(p), every diagram appears at once, and dragging a parameter slider moves all of them together. There is no project to set up, nothing to install, and no backend — the whole thing runs client-side in a tab.
That immediacy is the pedagogical point. The distance between a formula and the behaviour it describes is where control theory is usually lost, and it closes much faster when a coefficient is something you can pull on and watch respond than when it is a number you resubmit.
Result
Where this project ended up
Once the first version was finished, I licensed it to physics & engineering professor in France who wanted it as an add-on for their course website. It was the first money I ever made on the internet, and it ended up paying for part of my university.
A while later I found out the project had been forked by researchers at a Swedish engineering school, who built on it to teach their own students. It is also cited in one of the research papers that came out of that work: read the paper.