USB_ModeSwitch is (surprise!) a mode switching tool for controlling "flip
flop" (multiple device) USB gear.

Several new USB devices (especially high-speed wireless WAN stuff, there
seems to be a chipset from Qualcomm offering that feature) have their MS
Windows drivers onboard; when plugged in for the first time they act like a
flash storage and start installing the driver from there. After that (and
on every consecutive plugging) this driver switches the mode internally,
the storage device vanishes (in most cases), and a new device (like an USB
modem) shows up. The WWAN gear maker Option calls that feature "ZeroCD (TM)".
