> What technology do you use today that is far from mainstream?

Pen and paper. ;)

Also, I have been using an agenda with on the left side the week, and on the right side notes for the last 10 years. It has a special holder for a pen, contains some information on units, UTC differences, a world map, holidays, year overview, and much more. This is very useful. At work I only have to carry around my agenda. It contains all information that you need directly in meetings. And I can take notes on the right side that I can process (digitally) when I'm back at my desk.