Interesting C library for the nrf24l01. Why is this important? Well the chip is pretty cheap and gives you 2.4 GHz wireless (think older WiFi and wireless phones). You can get “boards” that support this from sparkfun for around $20. Or even cheaper on ebay. There is a nice tutorial on the chip in the one link below
http://dangerousprototypes.com/2013/05/01/portable-nrf24l01-library/
http://www.diyembedded.com/tutorials/nrf24l01_0/nrf24l01_tutorial_0.pdf