The greatest invention of all must surely be writing. It is not just one of the foundations of civilisation: it underpins the steady accumulation of intellectual achievement. By capturing ideas in physical form, it allows them to travel across space and time without distortion, and thus slip the bonds of human memory and oral transmission, not to mention the whims of tyrants and the vicissitudes of history.
Tom Standage argues that writing is the greatest invention of all time. I have to agree. Who needs wheels when you have books that can teach you about, well, wheels!