CAN Bus
I got my ELM usb adapter from SECONS in Prague, around 100 years ago. You can tell it's old by the brass and mahogany case it's in. Also the fact that it uses a USB mini connector.
See also tenrec not 8track, which has been gone for a decade.
2022-12-10 back looking at this, at least a hundred years have elapsed (Linux time) since I started this page.
CAN interfaces
Pi-CAN http://raspberrycan.blogspot.com/2012/08/controller-area-network-can-mcp2515-for.html
eDash
Circuit Cellar article: eDash Robin Brophy Sep 2011 issue 254
microOBD
Sparkfun UBM32 controller: USB 32-Bit Whacker - PIC32MX795 Development Board $40
320x240 LCD
Resources
Elm Electronics the folks who make the interface.
OBDtester and pyOBD
OBD Auto Doctor Free and paid versions, including Linux. The paid version is $20 per year.