Before the birth of Durango·X, several other attempts were made, with varying degrees of success.
SDd / Chihuahua
Originally standing for Didactic Development System, was a simple 1 MHz CPU 65C02 + VIA 6522 computer on a breadboard, intended to teach Hardware Fundamentals in the vocational school. Not all address pins were conected, thus limited to 4 KiB ROM and 2 KiB RAM.
Actually my first working 6502 design.
Chihuahua was essentially the same design on a compact protoboard, but there was some strange bug that prevented proper communication between CPU and VIA. An improved Chihuahua PLUS with full addressing range was started, but never finished.
There is a revival of the Chihuahua concept with some interfaces from the Durango·X computer.
The original Durango incarnation intended as a CPU tester, then an external VDU was added thru a preliminary IOx bus. Originally a 1 MHz, 32 KiB RAM, 16 KiB ROM system, soon was expanded to 32 KiB ROM with the familiar 128-byte I/O area. The external VDU was monochrome, 128 x 128 pixels.