The Broadcom processor used on the Raspberry Pi supports 3.3v SPI, which makes it trivial to attach a RFM69 with no other components.
The Pi makes a good Ethernet-enabled gateway, which is easy to remotely manage.
Russ has a very simple hat-like PCB for neatly attaching a RFM69 to the Pi: https://github.com/russss/raspberry-pi-rfm69
Alternatively, the Slice of Pi prototyping board has some 2mm spaced holes (intended for an XBee style module) which make it relatively easy to attach an RFM69 as shown here. This can be used on older Pi boards with the 26 pin GPIO connector as well as newer ones with the 40 pin connector.
There are currently three pieces of software designed to interface with an RFM69 Module connected to a Pi.