Mathematica Online is a new offering that allows for access to Mathematica fully via cloud, so no installation of software is needed. It is very versatile and can perform tasks including computing and manipulating calculus equations, plotting and modeling engineering problems, matrices and linear algebra, and more.
Hands-On Start to using Mathematica Online.
Working with Cloud Notebooks.
Mathematica Online Support.
Documentation for Wolfram Language & Syntax.
View instructions on how to find your specific MathID.
View instructions on how to obtain a new password for a previously registered Mathematica user.
Referenced from: http://www.wolfram.com/mathematica