Single board computers
I count as an SBC any board that can run an operating system like Linux or Android. Boards that can't are microcontrollers, even if they have 64-bit processors. Arduino PIC Feather Teensy, including Teensy USB Development Board
From the MQTT book; I think this are all SBCs but have not checked yet. I love the names.
- Qualcomm DragonBoard 410C
- MinnowBoard Turbot Quad-core
- LattePanda 2G
- UP Core 4GB
- UP Squared
Older notes
PC Engines makes ALIX (full schematics available) and WRAP (end of life) boards.
ALIX.3D1 system board (LX700 / 128 MB / 1 LAN / 2 miniPCI, rs232) $101 ALIX 3D2 system board (LX800 / 256 MB/ 1 LAN / 2 miniPCI, 2 usb, rs232) $115
Soekris boards are also popular for WiFi projects. None look interesting to me.
Mikrotik RouterBoard I experimented with a Mikrotik RouterBoard 532A (about $200 including a case and power supply).
PepLink makes load balancers, WAPS, and a general purposes gateway router/switch box calld the Manga. See also "Debian in 3 watts". This shows how to set up a Manga to run Debian from a USB storage device.