Transverters are devices that allow you to use your existing (often 10 meter) radio to operate on other bands for which there may not be a wide selection of radios, such as the 222 mhz, 900 mhz, 1240 mhz bands.
Using your existing radio, by connecting a transverter, your 10 meter radio will now transmit and receive on another band.
This is especially handy for someone who would like to operate 222 SSB since there isn't much in the way of allmode 220 rigs around.
DownEast Microwave manufactures transverters.