Another FOSS option is maxima, although like everything else in maxima, support for group theory is a bit weird and isn’t exactly comprehensive. https://maxima.sourceforge.io/docs/manual/maxima_151.html and https://maxima.sourceforge.io/docs/manual/maxima_147.html#It...
And on the paid side, if you have access to it, mathematica has group theory support also and a bunch of named groups implemented right out of the box including the Monster group and the Conway groups https://reference.wolfram.com/language/guide/GroupTheory.htm...
If you know Mathematica syntax, you could also try Mathics:
GAP and MAGMA a worth a look (GAP is included in other math software, eg: SAGE and is open source, MAGMA is commercial with education discounts and free student options)
* https://en.wikipedia.org/wiki/GAP_(computer_algebra_system)
* https://en.wikipedia.org/wiki/SageMath
* https://magma.maths.usyd.edu.au/magma/
* https://en.wikipedia.org/wiki/Monster_group