An ARM based credit card sized linux system for USD35. Runs Squeak very nicely.
See http://www.raspberrypi.org for the full details, their blog and forums.
The 2017 model is a quad-core ARMv8 1.2GHz cpu with 1Gb of ram, 4 usb2 ports, an ethernet port, wifi and BT, a line-out socket, two specialised connectors for an lcd panel and camera, HDMI and the infamous micro-usb power connector. It runs the full Cog/Spur VM quite fast.
The 2018 model 3B+ boosted performance with faster (1.4GHz A53) cores, faster ethernet and dual band wifi.
In 2019 the Pi 4 offers significantly faster 1.5GHz A72 cores, 1/2/4Gb of ram, USB3, fully gigabit ethernet, BT5LE and dual hdmi display outputs.