sniffing

• http://travisgoodspeed.blogspot.com/2011/02/promiscuity-is-nrf24l01s-duty.html
• http://goodfet.sourceforge.net/clients/goodfetnrf/

Alternative implementation

• http://sarwiki.informatik.hu-berlin.de/R0ket_Keyboard_sniffer
• https://github.com/Kaczmarczyck/r0ket/blob/486d3e07b08f185346a41a79e485f2999ddaf2ea/firmware/applications/radi0.c

Arduino libraries

• https://github.com/aaronds/arduino-nrf24l01
• https://github.com/maniacbug/RF24 (has private functions for register access, not suitable for sniffing)

MCU independent

• https://github.com/kehribar/nrf24L01_plus