LaTeX is a high-quality typesetting system, with features designed for the production of technical and scientific documentation. LaTeX is the de facto standard for the communication and publication of scientific documents.
My LaTeX Previewer is useful for experimenting with LaTeX without having to deal with many of the intricacies of the compile process.
My PNG/JPEG (Raster) to EPS/PDF (Vector) converter is useful for converting raster images to EPS/PDF for inclusion into LaTeX documents.
MetaPost is a powerful graphics language (by John Hobby) based on Donald Knuth's METAFONT, but with PostScript output and facilities for including typeset text. Knuth says that he uses nothing but MetaPost for diagrams in text that he is writing.
My MetaPost Previewer allows users to test MetaPost (similar to the above listed LaTeX Previewer) and generate EPS, PDF, and SVG output for the graphics.
My Function Grapher uses MetaPost and allows users to easily graph functions, parametric curves, and surfaces.
You can also find some of my accumulated MetaPost documentation and examples here, and in particular, my own suite of MetaPost tools.
Here is a loan calculator that I wrote for computing the principal, payment amount, interest rate, or term for loans with compound interest.