Maltron keyboards originated in the early 1970s when inventor Lillian Malt and entrepreneur Stephen Hobday collaborated to address ergonomic concerns with traditional keyboards. In 1976, they unveiled the first Maltron prototype, featuring a split, concave design and an integrated trackball. The innovative keyboard gained attention, leading to the founding of PCD Maltron Ltd. in 1977. Known for their
ergonomic excellence, Maltron keyboards have since evolved to cater to diverse user needs, setting a benchmark in ergonomic design and inspiring advancements in comfortable and sustainable technology interaction.
Check this video old video and Bueny.
and this Rare footage of Lillian Malt talking about the Maltron keyboard: 

Founded in 1992, Kinesis emerged from the concerns of engineers and ergonomists regarding the rising instances of repetitive strain injuries (RSIs) among computer users. Focused on addressing the discomfort caused by traditional keyboards, they developed the Kinesis Model 100. This contoured keyboard aimed to promote a more comfortable typing experience by keeping wrists straight and minimizing ulnar deviation, forearm pronation, and wrist extension. The success of the Model 100 established Kinesis as a prominent player in the ergonomic keyboard industry.

The SafeType Ergonomic Vertical Keyboard, introduced by a company founded in 1993, featured a distinctive design that positioned hands in a vertical, handshake-like position for improved comfort and to minimize wrist strain. This design aimed to reduce repetitive stress injuries and promote better ergonomics. The keyboard gained popularity for several years, but the company appears to have ceased operations in the mid-2010s. Despite its discontinuation, the SafeType remains a key example of ergonomic innovation.

DataHand Systems, Inc. was founded in 1985 by Dale J. Retter, specializing in innovative ergonomic keyboards. The DataHand Keyboard, introduced in 1990, featured a unique design where users could type by moving their fingers inside individual keycaps, reducing hand movement. It aimed to alleviate repetitive stress injuries. The company ceased operations in 2008, but the DataHand remains a notable example of early ergonomic keyboard design.

A Microsoft ortholinear prototype from the early 90s, incl. a trackball.  
Unfortunately, there are no official images of the Natural Ergonomic Keyboard. According to the patent application, the Natural Ergonomic Keyboard 8000 had an ortholinear layout with evenly spaced keys. The keys were arranged in a slightly curved shape, which was designed to conform to the natural curvature of the hands. The keyboard also included a trackball for controlling the cursor.
 

The NEC PC-8801-KI keyboard, from the 1980s, featured a unique column-oriented layout for its alphanumeric keys. This design was different from the typical row-based arrangement found in most keyboards of the time. It was designed for the NEC PC-8801 series, a popular Japanese home computer during that era.

The Apple Adjustable Keyboard, introduced in 1993, was an ergonomic keyboard designed for Macintosh computers with a split and adjustable layout to reduce wrist strain. It featured a customizable tilt for comfort during long typing sessions. While innovative, it had limited adoption and connected via Apple's Desktop Bus (ADB).

The microTRON (μTRON), designed by Dr. Ken Sakamura, is a compact, ergonomic keyboard developed for efficient and comfortable typing. It features a unique layout with minimized key movement to reduce strain. Also known as "MTRON" or "microTRON," it was designed to optimize typing speed and ergonomics.

The Datadesk SmartBoard UPC5000 (also known as the SB-5000) was an ergonomic keyboard released in the 1990s. It featured a unique design with a split and adjustable layout to promote a more natural hand position. The keyboard aimed to reduce strain and discomfort during extended typing sessions.