How different is it?

> While this has resulted in some incompatibilities between Macsyma and Maxima, programs written in the Macsyma algebraic language can often be run, with only minor changes, in either system.

Symbolic tensor manipulation is still supported https://maxima-on-wasm.pages.dev/doc/html/Package-itensor#Pa...

It's the only Macsyma anyone's running these days, so maybe if Symbolics hadn't killed it off there'd be another version more deserving of the title.