What are the best, similar to SPSS, quantitative tools available online and free out there for the analysis & demonstration of a quantitative research?
If you want something menu-driven, another option is Jamovi.
https://www.jamovi.org/
Here is a video discussing the relative merits of JASP and Jamovi.
https://www.youtube.com/watch?v=qhlXwY0mrZw
Personally, I think we ought to teach students from day 1 to use code so that their work is documented and reproducible. And I fear that teaching them to use code is not very easy using tools like JASP and Jamovi. YMMV. ;-)
PS- We also ought to be teaching some basic data management rather than just handing students pristine datasets that are ready to analyze. That does not prepare them at all for the real world of data analysis, where more time is typically spent on data management than on data analysis.
This is a question that has come up numerous times in RGate.
If all you seek is an spss work-alike (that is compatible for data files and syntax), have a look at PSPP, which includes many of the features of base spss (https://www.gnu.org/software/pspp/).
If you are making a "permanent" choice of statistical package, I'd strongly suggest you consider the R system. It's free, open-source, and available for multiple OSs, and there are more R libraries, which extend the types of analyses you can conduct, than for any other software base.
The Jamovi package, mentioned by Bruce Weaver, is very good for what it covers, and is built from an R framework.
Finally, you might consider having a look at these options, all of which are free (or, at the very least, free to try):