Supported Hardware
Host Computer
Unequivocally, Raspberry Pi. Read more...
PS: Not so fast. At the moment of original writing, a suitable Pi cost about $35, at the moment of writing of this, it is about x4 that. So let's revert to the original text that said "Any UNIX will do".
Sensors and Switches
All currently manufactured 1-Wire devices are supported. Most of devices that are directly usable have already been verified to work. If in doubt, contact Home Climate Control Forum;
Various DS2408 based relay boards;
Any hardware that can deliver its readings via stdout is supported. This includes all devices supported by lm_sensors, hddtemp, and vcgencmd;
XBee ZB based switches and sensors;
Pimoroni Automation HAT - product of choice for wired switches;
Most of sensors and switches exportable from Home Assistant, via MQTT integration.
1-Wire Adapters
Serial 1-Wire adapter (both pure serial and USB to serial such as LinkUSB is currently natively supported;
Pure USB 1-Wire adapter (such as DS9490) is NOT supported;
Servo Controllers
All servo controllers supported by Servomaster project are supported natively. This includes some historical Phidgets, most Pololu and Parallax controllers and some others in compatibility mode.
Protocol Adapters
Cables Unlimited USB-2920 USB 2.0 to Serial DB9 Adapter or any other FTDI based USB to serial adapter;
SABRENT SBT-USC1K USB to Serial (9-pin) DB-9 RS-232 Adapter Cable - supported, but not recommended, as well as other Prolific (PL2303) or Silicon Labs (CP210x) based adapters in general - they lack serial numbers, and having more than one adapter on the same host will be messy.
How To Get Your Hardware Supported
Three ways:
Wait until project contributors become interested in your hardware and support it;
Donate the hardware so project contributors can provide and test support for it;
Make a donation so project contributors can exercise their discretion and choose what hardware to support so you can reap the benefits.