TeX

TeX (more correctly written as TEX) is a computer typesetting system written by Donald Knuth, primarily for typesetting mathematics. It is a sophisticated typesetting engine with a powerful macro language. Probably the most popular system for computer assisted typesetting of scientific texts, it is often used even for non-scientific purposes, including artistic design. Literally thousands of macros and macro packages were developed by users of TeX, probably the largest and most famous being Leslie Lamport's LaTEX, and Hans Hagen's ConTEXt.

I made couple of small contributions to the large amount of TeX related software that is available:

• IpePlots is an extension for the Ipe graphics editor. It makes creating graphs of functions and parametric plots with Ipe easier. You can download IpePlots from github. The manual in pdf format is available here.
• The mathexam LaTeX package is designed to help one create simple exams for math classes. It makes leaving space for calculations and designating spaces for answer very easy. It is available on CTAN.