Loki was a concept computer to compete with the 16-bit machines at a low price point that was in circulation at Sinclair Research at the time they were brought by Amstrad in 1986.
Many of the features and design goals of Loki can be found in the Sam Coupé.
From http://rk.nvg.ntnu.no/sinclair/computers/loki/loki.htm
The Unreleased Sinclair Computers
When Sinclair Research finally threw in the towel in 1986 and surrendered its computer business to Alan Sugar's Amstrad, a number of projects were left uncompleted. As the Sinclair design team was disbanded, details of the projects inevitably leaked into the public domain.
By far the most interesting was the so-called "Super Spectrum", codenamed Loki. Depending on which account one believes, the name either derived from the Norse god (renowned for his love of games) or as a derivative of the acronym for Low-cost Colour Computer, aka LowCCC or LC3.
The Loki was intended to be an Amiga-beater, with custom graphics and sound chips, a "huge" 512x256 resolution in up to 256 colours and a 128K memory. The machine would also have a fully-buffered expansion bus, RGB, composite and TV display outputs, a serial port, two joystick ports, a light pen (supplied), three different types of MIDI port, stereo sound in and out, a headphone socket, and a video recorder/video disc interface. On top of all of that, floppy disk, hard disk, compact disk, mouse and modem connectivity would also be available. This remarkable package would cost as little as £200.
All of this was, of course, completely unrealistic and the specification amounted to little more than a wish-list. At the time, the Amiga, which was in some respects more limited than the Loki specification, cost £1,500. Much of that cost was due to its sophisticated custom-designed hardware. The Loki would have cost millions to develop over a period of several years (the Amiga took four years) and a £200 price point was far too low if the developer expected to make any money back.
In the event, the machine appears to have got no further than the design phase and was abandoned by Amstrad. Interestingly, however, its concepts did come to fruition in a very different form. After the Amstrad takeover, two ex-Sinclair engineers, John Mathieson and Martin Brennan, set up their own company called Flare, drawing on the Loki designs to produce a new multiprocessor games console. Atari were drawn into the project and, seeking to challenge the Sega Genesis/Megadrive and Super Nintendo, brought the machine to the market as the Atari Jaguar.
According to Jaguar developer Andrew Whittaker, "Some of that [Loki] technology also found a home in a machine called the SAM Coupé, which was manufactured and produced in the UK by MGT technologies (Bruce Gordon and Alan Miles, both ex-Sinclair staff also). It shared many interesting features with the Jaguar in terms of its video chip, but the machine sold very badly in Europe and the company folded."
From https://en.wikipedia.org/wiki/Loki_(computer)
Design
According to an article published in Sinclair User magazine, Loki was to have a 7 MHz Z80H CPU, a minimum of 128 KiB of RAM and two custom chips providing much enhanced video and audio capabilities compared to the ZX Spectrum, but with a compatibility mode. The video chip, referred to as the "Rasterop" chip, would have blitter-type functionality and three different modes: 512×256 pixels with 16 colours, 256×212 with 256 colours, or 256×212 with 64 colours and two bits per pixel used for "blitter objects". Comprehensive peripheral support was also claimed, including MIDI, lightpen, joystick and floppy disk. A version of the SuperBASIC language from the Search: “Sinclair QL” was to be provided in place of the old Sinclair BASIC for the ZX Spectrum and support for the CP/M operating system was also intended. On top of this, the computer would cost as little as £200.
Another Spectrum magazine, Crash, poured scorn on the report in Sinclair User, dismissing the design as "dreamware" in the opinion of an ex-Sinclair designer they consulted, analysing the implied components and costs, and adding, "It may be fun to dream about Loki, but the fact is that it won't appear, and nor will anything like it." This was the rationale, according to Crash Technical Editor Simon Goodwin:
Being blessed with lots of headed typing paper and very little money, the Thinkers at Sinclair were invited to make a big list of trendy computer features. That list, embellished with a few charts and tables but a noticeable lack of circuit diagrams and real detail, finally escaped into the hands of the computer press. Despite six years of agonising experience of the difference between Sinclair specifications and reality they swallowed it whole. Technical know-how has never been a strong point in magazines that still—indeed, the same month—print Commodore 64 screen shots in their Spectrum software preview section.
History
When Search: “Amstrad” bought out Sinclair's computer business in 1986, the project was cancelled.
Martin Brennan and John Mathieson, two Sinclair engineers, took the Loki technology with them and founded Flare Technology. There they worked on the cancelled Konix Multisystem game console, then later worked with Atari Corporation on the Panther (cancelled) and Jaguar systems. According to Jaguar developer Andrew Whittaker, two other Sinclair employees, Bruce Gordon and Alan Miles, who went on to form Search: “Miles Gordon Technology”, also used some of the designs in the SAM Coupé.