In most of the projects the XBee modules appear as interfaces, serving only for the wireless connection, but the they can do much more, they have seven analog input channels, nine digital I/O channels and two PWM outputs, it is almost like a micro controller the difference is that you can’t actually load your own control firmware, this needs to run on the PC, but this can be taken as a feature used in your advance since you can make complicated applications in any language and communicate over the serial port. The USB to serial converter should be a problem because the operating system will use it as a virtual serial port, no USB programming required.
With this advanced inputs and outputs you could make complicated robotics applications, smart sensors, and even closed loop systems, not being limited by the code size and speed only your imagination is the limit.
These features of the XBee are available only with the latest firmware version 10A1, if your module is older than you need to update the firmware.
Standalone XBee: [Link]