The Byfrexians are a spacefaring species.

The Byfrexians were enemies of the Sindareen, who waged war on them at their own cost. In 2368, the USS Enterprise-D was assigned to take Byfrexian delegates to Sindar for peace talks. (TNG novel: Imzadi)

The Byfrexians use calvinum to power their engines. Prior to 2369, Glav had discovered large deposits of the mineral on Xerxes III and sold it to the Byfrexians, being paid two million bars of gold-pressed latinum for the supply of the calvinum. (DS9 novel: The Siege)