I am looking for a qwerty, flat keyboard with the shortest travel distance and lowest actuation force possible. In other words, a keyboard that requires as little force as possible to type. The keyboard I'm looking for does not need to be mechanical, though.
Price and shipping locations are not an issue. (and it should be a keyboard, not a speech recognition software or some BCI device)
I know that the Cherry MX Red has 45 centinewton (cN) of actuation force but I find the travel distance to be too long (2mm to actuation, 4mm to bottom). I could customize the keyboard to be 2mm to bottom but that would be quite tedious, all the more so as I need more than one.
All other Cherry MX have pretty much the same travel distance:
A few more comparisons from http://www.pcper.com/reviews/General-Tech/Mechanical-Keyboard-Switches-Explained-and-Compared:
(they seem to mostly sell in Japan)
Some specifications regarding the Topre Realforce 104UB Silent:
The Romer-G Mechanical Switches have a lower operating point (1.5 mm) and key travel (3 mm).
They are present in the Logitech G910 Orion Spark RGB Mechanical Gaming Keyboard (920-006385)
In the following graph, the blue curve is a Romer-G Mechanical Switch, the white curve of is a typical mechanical switch:
The newly released (June 2016) Tesoro’s Low-Profile 'Agile' Switches are quite interesting: the full travel of the switches is 3.5 mm. Unfortunately, they haven't announced the actuation force nor the operation point. video
The ErgoDox EZ (open source, released in 2015) has a 35 cN key switch but the travel distance is still 2 mm:
Lastly, I have run across the Comfort Keyboard Split Magic Keyboard USB1-2BLK, as well as its non-compact version the Soft Touch ErgoMagic Keyboard.
It looks quite thin but According to one seller (Sam@fentek-ind.com, Monday-Friday 8a-4p Arizona MST, P: (928)639-0161 F: (928)639-0551) the key travel is 3.5 mm, and I don't want a split keyboard. (the seller also told me "we do not have a no split version of that keyboard and I do not have a plot of the key force and travel.")
There is a compact version:
As well as a non-compact version: