The Colour Maximite is a small and versatile single chip computer running a full featured BASIC interpreter with 128K of working memory and eight colours on a VGA monitor.
It will work with a standard PC keyboard and because the Maximite has its own built in SD memory card and BASIC language you need nothing more to start writing and running BASIC programs.
You can either build it yourself, or buy a prebuilt kit. This seems like a great DIY project.
RetroBSD is supported on that hardware: http://retrobsd.org/wiki/doku.php