Sure, your phone is fun, but if you want the fun and power of a full-fledged Linux computer in your pocket, you'll need to look elsewhere. The Mecha Comet is a 3.4-inch rectangular handheld that vaguely resembles a BlackBerry, but runs Debian Linux OS with a custom, touch-friendly UI on top. Launching soon on Kickstarter for $159, the device has a pogo pin interface where you can attach various extensions, including a gamepad, a Blackberry-style keyboard and a GPIO (General Purpose Input / Output) connector with 40 female pins.
Using the GPIO connector, you can attach a variety of electronic devices, including Raspberry Pi HATs. You can also attach HATs directly to the Comet or design your own extension board to attach to the pins.
