I drive a 2002 Porsche 996 Targa. Cars from that era talk to the outside world over a single wire called the K-line, and the tools that speak to it are either dealer equipment or aging Windows software with per-car licences.
So I started pdiag, an open, modern diagnostic tool for the water-cooled Porsches built roughly between 1997 and 2008: the 986 Boxster, 996, 997.1, 987.1 and the first Cayenne.
It reads the engine computer: live data, fault codes, identification, and the over-rev history that tells you whether a previous owner missed a shift. The web UI is built around a 996-style tach with those over-rev ranges painted on its rim, so live rpm and stored history sit on the same dial.
Two rules shape it. It is read-only: no coding, no flashing, and on purpose no clearing of fault codes, because erasing evidence is the last thing a tool used before buying a car should make easy. And it is clean-room: every identifier is decoded from my own captures, never from leaked dealer software.
Honest status: phase 0. The protocol stack, command line and web UI all run against a simulated car, with placeholder values. The cable is on its way, and the first real conversation with the 996 comes next.
GPL-3.0. The most useful contribution right now is data: a capture of another tool reading your car, with notes on what it showed.