Lots of popular calculators for graphing, calculating area, currency, percentage, etc.

An online scientific calculator useful for problem solving covering algebra, trigonometry, chemistry, etc.

Maple is a math software useful for education and research purposes. This software covers multiple areas of mathematics such as algebra, calculus, linear algebra, physics, statistics and data analysis, etc.

Microsoft Mathematics provides a set of mathematical tools that help students get school work done quickly and easily. With Microsoft Mathematics, students can learn to solve equations step-by-step while gaining a better understanding of fundamental concepts in pre-algebra, algebra, trigonometry, physics, chemistry, and calculus. Microsoft Mathematics includes a full-featured graphing calculator that’s designed to work just like a handheld calculator. Additional math tools help you evaluate triangles, convert from one system of units to another, and solve systems of equations.

Wolfram Alpha is a computational knowledge engine. It is not a search engine; rather, it generates output by doing computations from its own internal knowledge base.

The best way to get an idea of Wolfram Alpha's scope and capabilities is to view its Examples page.

Calculates the integrals of functions.

Wolfram Mathematica: Step-by-Step Derivatives