SymPy is a Python library for symbolic computation. It provides computer algebra capabilities either as a standalone application, as a library to other applications, or live on the web as SymPy Live or SymPy Gamma.
License: Open Source
SymPy is a lightweight library focused on symbolic mathematics and easy integration into Python, while Sage provides a more comprehensive mathematical framework with extensive features for both symbolic and numerical computations, albeit with a steeper learning curve and greater resource requirements.