Forge

A Forge is a volcano that appears to be an important part of the Sburb sessions.

The player living next to the Forge will eventually have to stoke it up. The planet of said player seems to be designed so that the Forge will bring about massive planetary change.

It is yet unknown if it has any other purpose. It may have something to do with the Ultimate Alchemy.

Kids' Forge
Jade lives next to the kids' Forge, as evident by its transition to her planet when she arrived in The Medium. In this page of homestuck and the two previous, Dave and Jade are shown to have ignited the volcano, melted the snow, and rescued some frogs coloured as the kids' respective text colours. Soon after, Bec Noir is seen teleporting in over the volcano.

Hephaestus, Dave's Denizen, wants access to the Forge so that he can repair the Caledfwlch that Dave broke.

Trolls' Forge
Kanaya lives next to the trolls' session's Forge, which is buried under the sands of the desert. It was transported to the Land of Rays and Frogs with her when she entered the Medium. According to Karkat, she uses this forge to destroy the Black Queen's ring to prevent Jack Noir from getting it.

Kanaya expresses frustration at igniting the Forge.

Trivia
Kanaya's destruction of the Black Queen's ring in the volcano-like Forge is a reference to The Lord of the Rings, whereupon the One Ring must be cast into a volcano to be destroyed.