Once upon a time, Clive Sinclair had a very fine little starter computer whose design he had financed and for which he was later knighted by the British Crown. The computer was the fine ZX80 computer and it was the least expensive complete computer at the time. Sir Clive next ordered yet another computer that would be even more inexpensive and yet more capable. The result was the Sinclair ZX81.
The fabrication of these ZX81 computers was outsourced to an American company that was known for its watches: the Timex Company. As part of this agreement, Timex would be allowed to market the computer design in the United States and chose to brand the resulting computer "Timex Sinclair 1000". The resulting computer, no matter the name, was the most inexpensive of all time and allowed many a person of limited means the ability to own and program their own fully-functioning computer.
I have owned two Timex Sinclair 1000 computers in my time, the first bought at surplus and in poor condition and ultimately unworkable. The second was given to me by my maternal foster-uncle and has, over the many years, been modified and expanded (which is a simple matter) and remains in my possession at this time.
In my experience, I can only say that the ZX81/TS1000 computer is a practically perfect fusion of economy and ability. Even today, it is a simple matter to build a home-made and fully-functional version of this computer with commonly-available parts; the firmware, with its version of the BASIC programming language, was released into the public domain and is readily available; and the construction and programming of the device continues to be a wonderful tutorial on basic hardware and software design. I wholeheartedly recommend this wonderous and tiny contraption to all with any interest at all in electronic computation.
Here is a wonderful webified ZX81 emulator!
ZX81 Rules OK!
Someone took great pains to render the ZX81 manual for the web, so I did the added honor of putting that site here on my own server, so that it will never be lost.