Regarding RT Systems's cables. I got one when I first got my VX-8DR. They were really the only source at the time for the connector.
RT Systems are using the FTDI chip but have assigned a custom USB Vendor ID and Product ID to it. Under Linux you can use this cable (and I do use it with Chirp) by telling the ftdi_sio driver the additional VID/PID to look for. I have a UDEV rule that I believe handles this.
Edit /etc/udev/rules.d/99-custom.rules contains customer udev rules # RT Systems cable for Yaesu VX-8DR SYSFS{idVendor}=="2100", SYSFS{idProduct}=="9e50", RUN+="/sbin/modprobe -q ftdi_sio vendor=0x2100 product=0x9e50"
This can also be done manual, by unloading (rmmod) the ftdi_sio driver are reloading it with the addition IDs as an argument.
rmmod ftdi_sio modprobe ftdi_sio vendor=0x2100 product=0x9e50
In the CHIRP repository there is something similar for an ICOM usb connection in the tools directory, see icomsio.sh.
There is a way to do this on windows with .INF files but I've never gone there and I'm afraid experimenting might be more trouble than it's worth for me.
An alternative that I've never tried but have seen described for other stuff that uses FTDI chips is there is a utility that can be used to change the VID/PID along with some other parameters. So if you've wound up with an RT system's cable but don't want to use their software you could always set the VID/PID
Note: I used to think RT System's going the proprietary route was for lock-in purposes. After reading one of the Wouxun yahoo groups for a while, it seems like 50% of the messages are related to problems with serial programming. By using the FTDI chip and a custom VID/PID RY Systems has probably eliminated 90% of the support calls they would get, so I don't really think of it as intentionally handicapping any more. There is no ambiguity about which COM port the radio is on.
Sorry for the stream of consciousness, maybe this will help someone.
--Rob