K-type
In theory I have one of these on the way:
	
	
	
		Code:
	
	
		https://input.club/k-type/
	 
 I qualify that because Mass Drop & Input Club are quarreling over ownership of Halo key rights.
In theory this will be a truly 'open' keyboard - but the legal wrangling seems to contradict that vibe.
Vortex Core
I have one of these.  Switching over to it proved to be... difficult.
	
	
	
		Code:
	
	
		https://www.amazon.com/Vortex-Core-40-Mx-Brown-Aluminium/dp/B01N6N6TJL
	 
 Typing sentences on it is pretty easy.  Gaming on it - wow is it difficult with anything that requires F1-F12 keys.
The firmware update fixes the Tab/Capslock key to put Tab on the top layer.
Overall quality - fantastic.  Novelty & nerd factor - off the chart.   Actual usability - Fn layer isn't printed on the keys - even the key mappings in the manual are wrong.  Mine has Cherry MX Brown keys and I've installed double o-rings to lessen the bottom out clack to see if I could make it 'tolerable enough' for an office environment - close, maybe - if I could ever get used to the super-compact layout.
If you search hard enough you will find that there is someone out there developing an open source firmware for it - I haven't tried it yet.
Unicomp EnduraPro
	
	
	
		Code:
	
	
		http://www.pckeyboard.com/page/product/UB40PGA
	 
 I bought one of these to see if it would be a viable replacement for my Thinkpad Ultranav keyboards.  I was wrong.
The pointer stick is like a floppy joystick stuck between the keys - not at all like the IBM Trackpoint mechanism.
The whole keyboard is plastic and more than a bit flexy.  Key feel is -ok-, but nothing like the quality of an IBM type M.
If you're looking at these expecting a steel chassis - nope.  Removable chord - nope.  It was a $100 disappointment.
Thinkpad Ultranav
I actually own 5 of these in various flavors.  Excellent keyboards to fit the compromise of a quiet office environment where anything that clicks is seen as offensive.
	
	
	
		Code:
	
	
		https://www.geek.com/chips/review-lenovo-thinkpad-ultranav-keyboard-724321/
	 
 I have:
2 'full sized' with the number pad on the right with 4 symbols per key & 3 of them in Chinese.
2 'compact' without the number pad with 2-3 symbols per key with 1-2 of them in Tiwanese (?).
1 'compact' without the number pad and the trackpad & trackpad buttons dumbed out to a flat dumb pad - not really an ultranav at that point.
IBM Type M
	
	
	
		Code:
	
	
		https://en.wikipedia.org/wiki/Model_M_keyboard
	 
 I have several full sized type M PS/2 port keyboards.  Wicked fast to type on once you get used to them.  Unacceptable in most quiet offices now due to the insanely loud but great feel tactile click mechanisms.
I also have one 'Type M Compact' that came from a PS/2 Model 25 (monochrome, no HDD) computer I used to own.  The best compact keyboard I've ever owned - but again, unusable in any modern office environment.
IBM Model F
	
	
	
		Code:
	
	
		https://en.wikipedia.org/wiki/IBM_PC_keyboard#/media/File:IBM_Model_F_XT.png
	 
 I have one of these - and the IBM 5150 PC to connect it to.  It doesn't get much use these days.
Quad Folding Keyboards
I own 3 of these.  One with a Palm Pilot / TRG Pro connector, one with a USB connector, one with bluetooth.
	
	
	
		Code:
	
	
		https://www.amazon.com/PalmOne-Portable-Keyboard-Palm-Handhelds/dp/B00004WHF9
	 
 
I also have a smattering of other keyboards & wireless keyboards, but those get even further from the topic here.
The 
@rygD link above to a 'Brand New Model F' keyboard - those aren't model F.  If it doesn't have F1-F10 on the left and a bi-level enter key, it isn't a model F.