Leo is a power tool for people who want to organize, study and work with data, especially complex data like computer programs, books, web sites and data bases. Leonistas say Leo is a revolutionary tool and that Leo is fun to use–even addictive.
Leo looks like other outlining programs, but it is not. This tutorial explains the difference.
There are four parts, plus a cheatsheet. Each part will take about 30 minutes to read. The last part is optional, and assumes some familiarity with programming in Python.