Back during the Wrath of the Lich King expansion, I wrote an addon for personal use that reminded me what I should be doing. I was running the Daily Dungeon on 7-9 alts at the time and needed help remembering things like Buffs, Mats, Stances, Presences, etc.
So I wrote RememberAll.
I updated it for Cataclysm, but stopped after that since I stopped playing as many alts in the raiding space in Mists of Pandaria and Blizzard removed many of the unique buffs and things I was tracking. They also added better messaging to tell players when they were forgetting something.
In Warlords of Draenor, several of my Dungeons and Dragons players were also guildies, and we had a discussion one night about how the Mine in the Garrison should play Diggy Diggy Hole. I laughed, said it was easy, and then they challenged me to do it. 30 minutes later (I discovered what SubZones were that night!) I sent them an addon that did exactly that.