Jack Eisenmann has really taken a common prototyping exercise to a fantastic conclusion with the DUO portable, a miniature 8-bit computer. With a full QWERTY keyboard, LCD screen, and Atmega 1284P on a single board, the DUO is quite pleasant to behold.
In his video he explains that he had previously enjoyed programming on a trusty old TI-84plus but found the keyboard to be a pain in the butt due to the ABCDEF layout as opposed to QWERTY. He notes that some IO pins would be a nice addition too. To solve this, he built the DUO, which not only has QWERTY, but also 17 I/O pins.
The DUO Portable
For programming, he has created his own language called Duo Portable Command Language, or DPCL for short. DPCL is plain ASCII that resides in the 12k of RAM available. As he runs through the process of writing a simple "hello world" program in the video, you can see that DPCL is quite simple and fairly strait forward. Of course you won't have to figure it out on your own; he's included the documentation on the computer as well!
If you want more details, like the microcontroller code, or want to read through the manual, you can find all the information on the DUO's website.