A collection of useful online
softwares:
These websites may not substitute professional softwares
Matlab/Mathematica/Maple, but it's very convenient when you're working
in a new computer.
- Wolfram
Alpha (extremely good if you want to solve an equation but forget
how to program)
- Bluebit Online Matrix
Calculator (solving linear equations, finding eigenvalues. Nice for
verifying your conjecture in spectral graph theory)