Overleaf - The online platform for scientific writing. Overleaf is free: start writing now with one click. No sign-up required. Great on your iPad.
PTC Mathcad - PTC Mathcad PTC Mathcad is Engineering Math Software That Allows You to Perform, Analyze, and Share Your Most Vital Calculations.
Fidus Writer - Fidus Writer is an online collaborative LaTeX editor especially made for academics who need to use...
SMath Studio - Tiny, powerful, free mathematical program with WYSIWYG editor and complete units of measurements support.
TeXworks - The TeXworks project is an effort to build a simple TeX front-end program (working environment)...
EngineeringPaper.xyz - Online app for engineering calculations. Solves systems of equations, checks and converts units automatically, supports plotting, and allows for the creation of a link to share your work. Free and open source, no registration required.