* Industrial I/O Subsystem A/D (Analog to Digital Converter) Devices
* Industrial I/O Subsystem D/A (Digital to Analog Converter) Devices
* GPIO (General Purpose Input/Output) Pins
* Raw HID (Human Interface Device) Devices
* I2C (Inter-Integrated Circuit) Bus Devices
* LabView LINX Remote I/O Devices
* PWM (Pulse Width Modulated) Output Devices
* Remote I/O Protocol Devices
* Serial Ports
* SPI (Serial Peripheral Interface) Bus Devices
* Stream Framing Protocol Devices
* TCP and UDP over IPv4 Network Devices
* Watchdog Timer Devices
Although libsimpleio was originally intended for Linux microcomputers such as the Raspberry Pi, it can also be useful on larger desktop Linux systems.
http://git.munts.com/libsimpleio/doc/RemoteIOProtocol.pdf
http://git.munts.com/libsimpleio/doc/StreamFramingProtocol.pdf
http://git.munts.com/libsimpleio/doc/UserManual.pdf