DietPi - Dietpi is a debian based operative system made to install new apps easyer.
Intel NUC - Intel NUCs are available as Kits(Barebones), Boards(Mainbaord only) and as perconfigured Mini-PCs.
TinyCore - Simple operating system based on Linux that uses "modules", and loads everything into RAM. Can be persistent too.
Udoo x86 Ultra - Udoo x86 Ultra is a modern PC, known as the most powerful X86 maker board and an Arduino 101 compatible platform.
DebianDog - DebianDog is very small Debian Live CD shaped to look and act like Puppy Linux.
Raspberry Pi - The Raspberry Pi is a tiny and affordable computer that you can use to learn programming through fun, practical projects. Join the global Raspberry Pi community.