Designs and simulation results are given for two small, special-purpose nanoelectronic circuits. The area of special-purpose nanoelectronics has not been given much consideration previously, though much effort has been devoted to the development of general-purpose nanoelectronic systems, i.e., nanocomputers. This paper demonstrates via simulation that the nanodevices and nanofabrication techniques developed recently for general-purpose nanocomputers also might be applied with substantial benefit to implement less complex nanocircuits targeted at specific applications. Nanocircuits considered here are a digital controller for the leg motion on an autonomous millimeter-scale robot and an analog nanocircuit for amplification of signals in a tiny optoelectronic sensor or receiver. Simulations of both nanocircuit designs show significant improvement over microelectronic designs in metrics such as footprint area and power consumption. These improvements are obtained from designs employing nanodevices and nanofabrication techniques that already have been demonstrated experimentally. Thus, the results presented here suggest that such improvements might be realized in the near term for important, special-purpose applications.