Sure you’ve heard of the Raspberry Pi, and the Beagle Bone Black… What about the PcDuino? CubieBoard? How about the MK802? Well they’re all small arm core powerhouse machines running embedded Linux. open-electronics has put together a neat comparison of all these systems. See how they all stack up to each other. Chipset, cpu speed, ram, storage, etc. One takeaway from the article is the fact that none of them really conform to any standard like they do in the PC world. So it’s important to pick the right board for your own application.
If you really are new to the game, surely you’ve heard of Arduino. Go check out this comparison of Arduino vs Raspberry Pi first. TLDR; Arduino: real-time, limited in some ways but quick to start; Raspberry Pi: not real-time, very powerful but more difficult to get started.