PTC Mathcad - PTC Mathcad PTC Mathcad is Engineering Math Software That Allows You to Perform, Analyze, and Share Your Most Vital Calculations.
Overleaf - The online platform for scientific writing. Overleaf is free: start writing now with one click. No sign-up required. Great on your iPad.
SMath Studio - Tiny, powerful, free mathematical program with WYSIWYG editor and complete units of measurements support.
TeXstudio - TeXstudio is an integrated environment for writing LaTeX documents.
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.
LyX - LyX is a document processor.