Todo.txt plain text file. Use Vim. Date and todo statement. Sometimes more for explanations. I never delete anything in it; just make an X next to todo’s I’ve completed. File goes back many years. I can easily search for something I did a long time ago.
And then there’s MS OneNote for capturing howto’s, quick script one-liners, cheat sheets, diagrams, notes on various industry interfaces, etc.
Then there’s SCM for bug, feature, and track tasking.
And usually notepad paper and pen for meetings, which if there are todo’s, go into my electronic todos.txt file.