DIY Auto Diagnostics, Any Open Source Solutions?

slaxx writes: As an avid tinkerer, I really want to collect as much data about my car as possible. Of course, using On-Board Diagnostics (OBDII) sounded great to me, but the price-tag of systems like AutoTap Scanner are a bit much for my college budget to handle. Are there any free, open source solutions available? What do Slashdotters do to tinker and record the inner workings of their own vehicles?