Trionic 5.5 is an advanced engine management system created by Saab Automobile. It uses ion current through the spark plug gap as a sensor for knock, misfire and synchronization detection
It has been completely reverse engineered by a group of enthusiasts who developed T5Suit, an easy to use program for tuning the Trionic 5.2 and 5.5 ECUs.
Using the ECU, engine wiring harness and sensors from a Trionic 5.5 Saab NG900, 9000 or 9-3 it is possible to transplant this system into the classic Saab 900 or use it as a stand alone system in a completely different car or vehicle.
There is even a twin Saab engine powered boat running Trionic 5.5 floating around youtube.
Usually these parts can be bought cheaply from a junk yard such as pick-n-pull, making this a cheap (And better preforming) alternative to many aftermarket ECUs.