If you just picked up a generic OBD-II – USB interface on eBay and have a Mac, it is true that it is generally more convenient to access these hardware on Windows. Even embedded device developers tend to use Windows to develop against these generic FT232R chip based USB-UART devices simply because of more available supports. But worry not, it can be done on Mac (really on Linux with a more open-platform framework than Windows), it’s just a bit more complicated since it tends to come in be open-source source code rather than prepackaged self-sufficient binaries.
But in this case, it’s not too bad. You can use pyOBD, an Python open-source project. You just need some packages from MacPorts
sudo port install py26-serial sudo port install py26-wxpython
Download and unpack the source code. And run directly with
p.s. you need X11