Wolfram Alpha is a powerful computational knowledge engine. It can perform nearly any mathematical task and is surprisingly easy to use.
Here are some basic math examples.
Here is a gallery of visual examples. (Showing more than just mathematical computations)
Linear Algebra Commands
You can enter matrices row-by-row:
This will return the matrix, its inverse, eigenvalues & eigenvectors as well as some other miscellaneous information.
If you wish to row reduce this matrix, you can type:
or augment the matrix:
Wolfram Alpha is very robust and powerful, so you can enter variables or mathematical constants and manipulate them. Experiment!