[babayega2]

Maxima is the clone. I remember using it 20 years ago. very nice.

[zozbot234]

It's more like both Mathematica and Maxima are clones of the original MACSYMA.

[pkaye]

Maxima is based on the DOE (Department of Energy) fork of MACSYMA.

[Y_Y]

Maxima is a similar CAS, but it's not a clone of Mathematica like Mathics aims to be.

[pfortuny]

Maxima, despite its shortcomings, is a great tool for symbolic computation.