Balance of the Planet

Trivia

Contrary to its predecessor Balance of Power, Balance of the Planet did not require Microsoft Windows; it was a genuine DOS program.

Balance of the Planet contained an excellent manual (written by Chris Crawford). It described most of the major ecological issues and problems in a compact and comprehensible way, and was perfectly suited as an eye-opener as well as a reference-book. Additionally, it included a section called "Quickie Math Refresher", which described the mathematical basics (from strange numbers to logarithms) needed to fiddle with the formulas in the game. My personal favourite is this nice distinction:
Sqrt: This stands for "square root." [...]
Sqik: This is what ducks do if you hold them in your lap.