fxSolver is described as 'Online math solver, equation library, graphing calculator and science/engineering problem helper' and is a popular Calculator in the education & reference category. There are more than 100 alternatives to fxSolver, not only websites but also apps for a variety of platforms, including Mac, Windows, Linux and Android. The best alternative is SpeedCrunch, which is both free and Open Source. Other great sites and apps similar to fxSolver are Microsoft Office Excel, Wolfram Alpha, Qalculate! and GNU Octave.
Omega Calculator is an intuitive and powerful calculator that can be used for any mathematical computation you need to perform. I built this calculator to be different. It's beautiful, free, and has no ads: the VERY BEST calculator I have EVER used.
CADWOLF is a web based collaborative engineering platform. Create documents with equations, plots, loops, etc. Direct link to CAD models with systems to build structures in part trees. All you need is a web browser.