The RF transceivers RFM69 are really nice for low power applications. There are many projects using it currently.
It supports FSK, GFSK, MSK, GMSK and OOK modulations. Also it has AES and CRC-16 engines internally.
I decide to list some projects here as future reference.
First project is called RadioHead (no! it is not the music band). The main advantage of RadioHead is because it supports many types of transceivers (nRF24, CC1100, MRF89, etc) :
http://www.airspayce.com/mikem/arduino/RadioHead/
The second project is from LowPowerLab, it is devoted exclusively to RFM69 family:
https://github.com/LowPowerLab/RFM69
Other project devoted to RFM69 is plainRFM69, this project has some optimization to enter on low power mode as soon os possible and doesn’t have all features from previous project:
https://github.com/iwanders/plainRFM69
There is an interesting thread from iwanders (Ivor Wanders is the author of plainRFM69) :
https://forum.pjrc.com/archive/index.php/t-27442.html
Another interesting project: Using a RFM69 to control a KaKu switch with OOK modulation:
http://members.home.nl/hilcoklaassen/
I receive some RFM69HW modules (bought from Alibaba) and my plan is to use it with NuttX, this transceiver has many features, then creating a Network Driver is not so easy. The datasheet is here: http://www.hoperf.com/upload/rf/RFM69HW-V1.3.pdf
Alan C. Assis 