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
Various DS2408 based relay boards;
XBee ZB based switches and sensors;
Pimoroni Automation HAT - product of choice for wired switches;
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;
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