RC2014
http://rc2014.co.uk/
As soon as you turn RC2014 on you can start programming in Microsoft BASIC.  This is very easy to get started with and some very complex programs can be written.  To get right down to the metal, though, you can write your programs in Z80 machine code.

Development of the RC2014 has lead to a more powerful machine with pageable ROM, 64k RAM, compact flash storage and a whole range of expansion peripherals.  With the right modules, it’s now possible to run CP/M, which opens the RC2014 up to a wide range of software.

RC2014 can be bought from Tindie:
https://www.tindie.com/stores/Semachthemonkey/