<p>To manipulate equations I use Derive, SymPy, Wolfram Alpha (tried pro, but it does not enable any longer equations than the free version), and Wolframscript from Wolfram Engine for Developers. I also use Octave (MATLAB clone) and mpmath for large-number stuff.</p>
<p>Please do not hesitate to edit my questions and answers.</p>
<p>I try to remember to write out every abbreviation and explain obscure mathematical symbols at the first mention. Also it is never bad to link to Wikipedia.</p>
<p>I vote also on answers that compete with mine.</p>
<p>I cross-license all of my code and images in Stack Exchange under <a href="https://creativecommons.org/publicdomain/zero/1.0/" rel="nofollow noreferrer">CC0 1.0</a>.</p>

Olli Niemitalo