Fuelly lets you share and compare your car gas mileage. You can track your own progress based on your driving conditions, changes, etc. You can even compare it with the EPA estimates and other people who own the same car.

Nested GUIs aka Microspaces is an interesting way of browsing the web. Unfortunately, it does not actually look too interesting to me and I do not see how useful it can be. It is actually still in private beta, and they are still trying to figure out what they want to name their company/product so it is obviously still a work in progress.

Yoono provides widgets that can simplify your web surfing and keep you connected with your friends. Yoono was one of the sponsors of the Summer Mashable events. The webnotes function looks cool and easy to use allowing you to easily drag and drop text, images, and videos from websites and share it with your friends. You can directly use Yoono to search for music and listen to radio stations as well. Personally, I am not a big fan of widgets, because even though they are suppose to make your life easier, I find it more complicated since you have to learn how to use the widget and get used to using it.