You can use an Anarduino board that has an atmel 8 bit micro (Arduino compatible) from Anarduino.com
or if you need more RAM/Flash and CPU, consider a Teensy 3.1 or 3.2 from PJRC.com or SFE. There is a piggyback PCB for using the same HopeRF radios as on Arduino boards, with the Teensy.