My favorite forgotten tech is the Garmin iQue, which is a PalmOS-based handheld GPS unit. Because of its color screen, its battery life wasn't great, so it wasn't suitable for backcountry use, but as a dash-mounted GPS is was great. While other GPS units at the time required you to navigate through confusing menus to enter an address or find a point of interest, the iQue allowed me to use Grafitti handwriting recognition, which was a lot faster.