Graphmatica - Free graphing software to download. Great for learning and teaching coordinate geometry and single-variable calculus.
Octave Online - Essentially free MATLAB that can execute uploaded files through an online terminal.
Symbolab - Want Wolfram Alpha with the free solutions back, and without the information overload? This is the simpler and free symbolic computation software.
Integral Calculator - A neat online tool that solves integrals with steps shown!
Linear Algebra Toolkit - Excellent calculator for reduced row echelon form with every step written out.
Matrix Calculator - Need to multiply two matrices instantaneously?
GeoGebra Math Apps - Great tool for teaching and learning algebra, geometry, and probability visually.
Geogebra 3D - An online three-dimensional graphing tool!
Simplex Method Calculator - Excellent and easy-to-use online calculator for linear programming.
Matrix Game Calculator - Easy to use matrix game solver. Unfortunately it doesn't show the steps...