I was given a really neat type of pen from Japan called a friction pen. It is Pilot brand, Frixion Ball Slim. It writes like a regular pen and has an eraser of sorts at the end. The eraser is a plastic ball that removes ink from the paper simply using friction and heat, and the plastic doesn't wear down on the eraser end. The pen looks like a slim gel or ballpoint - I have to play it with more.
I haven't seen this type of pen before. I was told that at warm temperatures the ink can disappear, but if the paper is placed in the freezer the writing will reappear?!