From their literature the RFduino is a stand-alone board like the Arduino UNO. In addition it has a powerful 32-bit ARM Cortex-M0 processor giving it more power than the UNO but enabling it to run the same Arduino code so there is no need to learn any new programming language or environment. Standard Arduino sketches run on the RFduino. Its GPIO lines support digital IO, analog ADC, SPI, I2C, UART and PWM. Its 7 GPIOs are software selectable and can be remapped as necessary. It has Bluetooth Low-Energy 4.0 built-in enabling it to talk to Smartphones and there are currently iPhone apps available, Android to follow. The RFduino is similar to the Arduino UNO or DUE but at a fraction of the cost and with wireless Smartphone connectivity built in.
The small finger-tip sized board uses 0.100” DIP headers which fit a regular solderless breadboard. Oh, and it costs $20.