The following link provides a list of items that the columnist suggests are some of the most underrated inventions. Such lists are subjective, but I enjoy reading them and considering whether I agree with the assertions that have been made.
The hard part in some respects is trying to get a consensus on what kind of recognition should be given in order to say that something was not underrated. Anyway, that is a different discussion.
Here is the list. Use the link above to try and understand his reasoning.
1. The chariot.
3. Horse collar.
6. Rotary printing press.
7. Barbed wire.