There's a very powerful new Open Source (hardware and software) embedded development board out from the makers of the Beaglebone series of boards.
The Beagleboard X15
This new board's specs read more like a low end Intel NUC board's specs (ok.. maybe not). But the kicker is, the boards are open source, and there are ONE HUNDRED AND FIFTY SEVEN GPIO pins. These are broken out on 4 60 pin connectors along the bottom of the board. That is a ton of GPIO. For Comparison the Arduino has 16 GPIOs broken out, and the venerable Raspberry Pi has 26 GPIO pins.
Additionally it has eSATA and HDMI outputs.
And for once (!) they helped out case makers by placing the outputs mostly along two opposite sides of the board (instead of all around it randomly).
Backing up all these inputs and outputs are a 750-MHz C66x DSP and a Quad-core PRU and a Dual-core Cortex-M4. That's 7 independent cores (aside from the main OS processor) on 3 processors working on real time response to inputs or program logic.
I haven't even mentioned the 2 Gigabit RJ-45 Network ports, making it a handy stand alone router.
It runs Debian out of the box (from its embedded flash memory), peripherals can be hooked up via USB 3.0.
Unfortunately it will be over $1 per GPIO, the prices being mentioned are in the $200 range.
Making it as much as an HP Stream Mini, but that's a very different animal.
I hope to see these boards used in some projects to do some seriously heavy lifting.
Like for example running all the operations on just this board for a Pick and Place CNC machine with 4 axis movement and 3 cameras and multiple spool controls. Or a drone with all the automatic features and multiple cameras.