Since I had a couple of ESP8266 modules on my bench, and hadn't found a use for them yet, I cobbled together a method to hook them up to my old PowerBook 540c.
It's just a Mac serial -> DB9 adaptor, connected to an RS232 TTL Level converter (from http://www.pollin.de, but they're easy enough to come by elsewhere too).
I had to hack the level converter slightly to add a 3.3v output for the ESP module (which isn't 5v tolerant). I then ran the MAX232 from the ADB port's 5v line,
and the ESP8266 from the 3.3v regulator. As you can see in the picture, the standard AT firmware is working fine!