The Aesir are a species appearing in the user-made Twisted Infinities campaign, named after the collective name for the elder gods in Norse mythology. Little has been released about their specific natures, but released campaign screenshots show their ships to have a characteristic blue colour and an often aerodynamic, modified delta shape. Aesir ships are named from Meso-American mythology and culture.
Several of the TI team have made comments that make it reasonably certain the Aesir are aquatic at least in a stylistic sense. They have been referred to as both "dolphins" and "plesiosaurs" so their actual nature is still very much unclear.