The 21st century realization of the C65 heritage: a complete 8-bit computer running around 50x faster than a C64 while being highly compatible. C65 design, mechanical keyboard, hd output, sd card support, ethernet, extended memory and other features increase the fun without spoiling the 8-bit feel. Hardware designs and software are open-source (lgpl).
http://mega65.org/
http://mega65.org/