As someone who is well-acquainted with both SMath and Mathcad, I am often asked which package is better.
I respond with a question to a question, something like this – which is better, an airplane or a helicopter? Both of these machines are designed to transport people and goods through the air and each has its advantages and disadvantages.
SMath and Mathcad are intended for calculations using units of measurement and the familiar notation of formulas.
About the advantages of SMath on the Mathcad forum
https://community.ptc.com/t5/Mathcad/Mathcad-vs-SMath/m-p/802499
Let's write together about the advantages of Mathcad on our forum!

1. Mathcad has Minimize/maximize functions

2. Mathcad can solve not only ODEs but also DAEs systems

Meanwhile, there is other competition than just Mathcad.

Recently I came across the following two. They are on github, run in the browser and come with decent documentation. Yet their document format is notebook style (vertical sequence of cells)

https://blog.engineeringpaper.xyz/ (symbolic algebra and calculus, non-standard unit formatting, nice coolprops-integration)

https://hurmet.org/ (support of formula display with substituted values)



The commercial tool https://blockpad.net/de/ has already been discussed here, if I recall correctly.



I am not suggesting to switch to these systems (yet for some users it might be the reasonable), but to get inspirations as to what UI features might be useful.

There's one, but significant, problem with these cloud calculators. At any moment, you and your entire country could be thrown out, along with all your calculations and history. We (in Russia) are now creating alternatives for everything we can cover and will never again rely on Western resources.

Whatever I could write on that topic would better be discussed face to face. Just some words. In his youtube channel "predictive history/game theory" Prof. Jiang predicted that Germany and Russia will come together in the aftermath of the US imperial overstretch. Whether this is a good idea or not depends on what Germany and what Russia we will have by then. The current hostile relation (or the lack of relation) is not to the benefit of either side.

As to the cloud software: Both open source programs can run locally, Hurmet actually is a progressive web app which remains available even offline. Probably, any deeper dive will reveal severe conceptual limitiations which might hurt as much as those in SMath. Yet, looking over the rim of the plate on your table (as we say in Germany) is always a good idea.