SageMath is free, open-source math software that supports research and teaching in algebra, geometry, number theory, cryptography, numerical computation, and related areas. Both the Sage development model and the technology in Sage itself are distinguished by an extremely strong emphasis on openness, community, cooperation, and collaboration: we are building the car, not reinventing the wheel. The overall goal of Sage is to create a viable, free, open-source alternative to Maple, Mathematica, Magma, and MATLAB.
Tutorial
The tutorial is the best way to become familiar with Sage in only a few hours. You can read it in HTML or PDF versions, or from the Sage notebook. Click here for a link to the tutorial site for Sage: https://doc.sagemath.org/html/en/tutorial/
Sage also includes a reference manual for Sage's many features: https://doc.sagemath.org/html/en/reference/
Support
Support for SageMath can be found on their website: https://www.sagemath.org/help.html