The Scottish Sgian-Dubh (skee-ən-DOO) "Black or Hidden Knife" is a dagger with no guard that was designed for concealed or low profile carry.
Typically it is worn tucked into the top of the kilt hose (tall socks) on the same side as the dominant hand, but they have also been concealed in the armpit.
Tradition and etiquette in Scotland called for leaving longer weapons (Claymore, axes, pole arms, spears, etc.) at the door when visiting or being a guest inside a home.
Carrying a Sgian-Dubh allowed one to still be armed and unnoticed while sitting at a table while enjoying whisky and haggis.
(Today we might do the same thing with our rifles and shotguns; leave them nearby, but still have a pistol on our person.)
Most of today's Sgian-Dubhs are ceremonial in nature; they are just mock ups or drones (pointy, but with a dull edge).
My Sgian-Dubh is a custom by Ken Brock and I really like it.
It has some contour to the grip, but no guard really to speak of.
I haven't had the chance to carry it with my kilt yet, but I look forward to doing so soon.