Math is Fun – Vector Addition Calculator
Decompose vectors into the x and y components, and add vectors using x and y components, or using magnitude and direction.
Reshish – Gauss-Jordan Elimination Calculator
Solve systems of linear equations using Gauss-Jordan elimination. This calculator can solve 20 equations and 20 unknowns, and beyond.
Ames – Projectile Motion Calculator (my favourite)
Omni – Projectile Motion Calculator (pretty good)
Solve projectile motion problems, relating time of flight, horizontal/vertical displacement, and launch/impact velocities
Solve quadratic equations of the form Ax² + Bx + C = 0.