MacUSBtoSerial
From SqueezeboxWiki
For some reason I haven't been able to get a serial connection between my Macbook and a controller for several months. I picked up a couple different USB-Serial adapters in an effort to remedy that situation.
Works
This adapter works. It has an FTDI chipset, and after installing the driver from the ftdi website, it works fine in OS X.
I might add that I discovered this as an alternative to Zterm. Great for the command-line-inclined:
/Users/bklaas: screen /dev/tty.usbserial-FTE1XN86 115200
note: ctrl-a ctrl-k to close the connection
Also, the Keyspan Adapter works for most people, but I should note that I went through this exercise started because I could no longer get my Keyspan adapter to work. YMMV.
Doesn't Work
This adapter does not work. It has a prolific pl2303 chipset. There is an OS X driver for this chipset, but while I could get the tty device to show up in the /dev list, I was unable to get it to work in either ZTerm or using the command-line screen.