There you can find 5 magical daggers for D&D 5th edition, converted from previous editions of the D&D game.
Dagger of Armor Piercing
weapon (dagger), uncommom
While you make an attack with this dagger, your opponent's armor and shield don't count for its AC, which becomes 10 plus any modifier granted by Dex or by magic items (magical rings or bracers or cloaks but not by armors or shields) or by spells, such as mage armor or shield or barkskin.
Dagger of Blackflame
weapon (dagger), legendary, requires attunement by a halfling
You gain a +2 bonus to attack and damage rolls made with this magic weapon.
As a bonus action you can extinguish all flames (normal or magical) you touch with this dagger, affecting a 5 foot radius sphere.
Absorbed flames charges the dagger at the rate of 1 for normal flames and 2 for magical ones.
It can store up to 10 charges and when it's full you can't extinguish flames anymore.
As an action you can release the flames in a line 5 foot wide and 40 feet long, originated from the dagger's tip. You release all charges, causing 1d6 fire damage per charge released to any creature or object stuck by the line. Creatures must make a Dex ST DC 15 to take half damage if successful.
Alternatively you can realese the flames if you attack and it a creature with this dagger. You release all charges adding to the normal damage of the dagger 1d6 fire damage per charge released.
Dagger of Defiance
weapon (dagger), very rare, requires attunement
While you're attuned with this magic dagger you cannot be frightened and you gain advantage on saving throws against being charmed and petrified.
Dagger of Doomwarding
weapon (dagger), very rare
You gain a +1 bonus to attack and damage rolls made with this magic weapon.
It has 7 charges. Once a round whenever you make an attack roll, an ability check or a saving throw and you've failed it you can use a charge to roll a again a d20.
You must take the number rolled by the second d20.
When you use the last charge, the dagger becomes a simple magical dagger +1.
Dagger of Sounding
weapon (dagger), rare, requires attunement by a rogue
You gain a +1 bonus to attack and damage rolls made with this magic weapon. While you are attuned with it, if you gently tap its tip against a hollow surface, it gives a resounding ring, quite different from the dull tone emitted if struck against solid stone. While you do it, you gain advantage in any Perception or Investigation check to find a secret door.
Dagger of Defiance and Dagger of Doomwarding are originally from the Forgotten Realms setting but you can easily import into your own campaign.
Dagger of Blackflame is from Mystara setting, and it's specifically from the Five Shires, the hin (halfling) realm of the Known World. Again you can import it into your campaign and you can replace attunement by halfling with a normal attunement if it doesn't suit well to your campaign.