There are many TeX packages available which provide functionality in areas not covered previously in this guide. A great resource for discovering new and interesting packages is CTAN's list of packages by keyword, linked below.
There are several interesting packages related to music available for TeX. A few are collected below, and be sure to look at the package documentation for instructions on their use. For a more comprehensive list, see the CTAN music page.
musictex package, which can be used to typeset polyphonic and orchestral music scores. This package is not available in the TeX Live distribution.gchords package allows users to create chord diagrams for the guitar. Options are available to draw them in any size, using any number of strings, produce black dotes or numbered circles to denote fingers, add chord names, show the number of the top fret, specify fonts for almost any symbol occurring in the diagram and many more. There is also a macro to typeset chords above lyrics.gtcrd package allows users to superimpose chord names over lyrics. Another package, guitar, provides similar functionality but gtcrd provides macros for transposing songs or sections of songs by a certain number of half-tones, as well as a few other interesting functions.piano package allows users to insert a small, 2-octave piano diagram with up to 7 keys highlighted. There is no documentation for its use, but the ReadMe file gives an example of how to insert the diagram.There doesn't seem to be a large body of resources available for TeX with engineers in mind, but a list of certain resources which may be useful is presented below.
pst-stru package is based on pstricks and allows for the drawing of structural schemes in civil engineering analysis. The types of figures which may be drawn include beams, portals, arches, and piles. Lots of graphical examples with accompanying code are given.circ package allows for the creation of circuit diagrams using LaTeX. It also has the functionality to create basic optics diagrams as well, though a more robust package for optics is linked below.