Relied on?
1969 Chevy shortbed.
A more techy thing in use every day is a really ****ty 286 single-board-computer I scavenged from work 10 or so years ago. It runs a very small IP firewall based on Minix 2.0 (the OS is on a floppy disk lol) that I needed at one point, but left in place because I'm lazy.