Officially listed but "non-typical" weapons in 5e, Abit of confusion.. If captured/looted, these 100% ok to use? They seem to be

Would the Thri-kreens weapons, the Gythka and the Chatkcha, count? In the MM, they're specifically described as special "martial weapons." Which to me implies that if a player got their hands on one of them, and was proficient in martial weapons, then they'd be able to effectively use them.

Quote from Heartofjuyomk2 >>

The shadar-kai shadow dancer and tlincalli have spiked chains that do a variety of neat things.

 Another interesting thing about the shadow dancer is that they're clearly using Dex for attack/damage instead of Str. Since their class abilities don't mention being able to use either Str or Dex for damage ala Martial Arts, I could see an argument for their spiked chain being Finesse.

I found a few more:

• Kender Skirmishers wield the hoopak, a spear with a slingshot attached to its handle.
• Pisonic Thri-Keens have two special weapons, the gythka (two-handed polearm with a blade at each end) and the chatkcha (a light bladed throwing triangle)
• Githyanki Knights carry a +3 "Silver Greatsword" that can cut the silver cord of an astral traveler.
• The new Thieves' Gallery statblocks have several unique weapons, like the daggersword or the darksteel greataxe. There's also a universal note that players aren't allowed to use them :P
• Kuo-toa Whips carry a pincer staff that auto-grapples small or medium targets on hit.
• Rakdos Performer, Fire Eaters wield a d6 spiked chain that has reach and finesse.
• Grimlocks carry a spiked bone club that deals blended bludgeoning and piercing damage
• Variant Ettercaps use a web garrote. (The only garrote in 5e if I'm not mistaken)

The hoopak is an official weapon now for PCs too.

Quote from IamSposta >>

The hoopak is an official weapon now for PCs too.

Oh cool! Not many melee/ranged hybrids in the game, that's a nifty little option :D