Mathematica is described as 'Definitive technical computing system spanning machine learning and neural networks, data science, visualizations and much more' and is a very popular numerical computation software in the education & reference category. There are more than 50 alternatives to Mathematica for a variety of platforms, including Windows, Linux, Mac, Web-based and Android apps. The best Mathematica alternative is SageMath, which is both free and Open Source. Other great apps like Mathematica are R (programming language), GNU Octave, Jupyter and Maxima.
Sage supports symbolic maths through Maxima