Nethership

Netherships are a mean of transport over great distances for large amount of people or cargo. They are used by the Golden Torch, which hijacked them from the Burning Legion, namely from Luxien while she was looking. Presuming they weren't able to take or destroy all netherships, some of them still remain in the possession of the Legion. Who created them, how do they work or what is fueling them remains unknown.

Traveling
Netherships are able to travel thorough both the Great Dark Beyond, like a normal spaceship, and the Twisting Nether. Navigating a nethership thorough the Great Dark is relatively safe, considering you can run into meteors or crash into a star, but slow, while flying thorough the Twisting Nether is very risky but fast. The Golden Torch travels long distances by doing many smaller jumps thorough the Twisting Nether, appearing in the Great Dark Beyond here and there, until they reach their goal.

Netherships seem to have emergency exits.

Starclaw
Upon materializing from the Twisting Nether this nethership was shot by the Burning Legion. Taedal managed to navigate it it on the Azeroth's orbit and then not so softly land on Pandaria. The wreckage can be seen at Descension Point. Giveen that Taedal used to steer and navigate this ship, it was probably his personal one.

Crown of the Skies
This nethership serves as Taedal's substitute personal nethership with which he offers the adventurers trips to Argus (on Winter Veil).

Star Racer
The nethership connecting Torchkeep to Larakamath. Adventurers travel on it as a part of the Larakamath questline. It is presumably Alirdus's personal nethership.

Mooneater
The personal ship of Keeper Damou, which upon arrival on Azeroth had been assaulted by Lich King Zener and his necromancers. Now it is anchored in nethership docks in Torchkeep and serves as a dungeon instance, not yet examined more closer, but very likely it is again invaded by the necromancers of the Dark Contract, which is why the ship isn't currently used.

Heaven's Wings
Flies from Heavenly Landing in Bonehills to Shadow of Theramore in the Veil.

Unknown
There are currently three active netherships of yet unknown name. They connect Torchkeep to Orgrimmar and Stormwind, and Scorch to Ka'reshan Fields.

Fleet
Three very big netherships known only as the Fleet are floating in the Twisting Nether west of Ka'reshan Fields and north of Bonehills. They are connected to each other with system of bridges and a big chain connects them to the Bonehills. It is a large open PvP zone for everyone who hit the level N+10, similar to Ashran. It is accessible either via a flight path or thorough a portal in Torchkeep