I'm still using an outliner called PC Outline 3.34. My manager gave me a copy in 1986, saying "Here, you're organised. You'll like this" and he was right. I bought a copy and have been using it every day since then for todo lists, shopping lists and functional decomposition. As it's an old DOS program, I have to run it in DOSBox on Linux or vDos on Windows 7.

I'm sticking with 3.34 as the 3.37 version has some bugs and the 1.00 version for Windows has a lot of them.