Here are a couple of amazingly thin erasers.
The Tombow Mono zero is a 2.3mm diameter cyclindrical eraser, dispensed by clicking the cap. It really does seem like a mechanical pencil in both form and function.
I thought this eraser was probably a borderline novelty, but it worked quite well over a period of days. You wouldn’t use it to erase several lines of text, but it is great for smaller tasks such as changing a line fragment, digit or letter.
I like the portability as well.
The Pentel Clic Eraser Hyperaser is a rectangular metal housed eraser. It has a dispense mechanism similar to that of most stick erasers, such as the Staedtler 528 50. A clip as well!
This is an ink eraser. It seemed to work well on tests with ballpoint ink, and less well with fountain pen ink.
I wasn’t expecting much, but both seemed pretty good.
The main problem I see it that both require yet more proprietary refill types. The Mono zero in particular seems like it will require a replacement eraser soon enough.
My thanks to der Lexikaliker for the Pentel eraser.