Instant portable whiteboards [Lifehacker]

Does this count as a gadget? No idea, but it's damned handy, especially if (like me) you're the sort of person who gets these urges to sketch things out of his head and onto somewhere he can point to them when explaining things. One startup I was involved with, many years ago, we put clear plastic sheeting all over one wall, and used that as the biggest whiteboard I'd ever seen. Hugely handy.