HEXAcoin, or just "HEXA", is the currency of the voxelcosm, accepted across all colonised worlds. It has no value in any other reality.
Once, it was immensely useful and some could buy and sell planets with it, but you know, the dataclysm happened and the currency depreciated to nothing. It is slowly regaining worth.
The term "HEXA" comes from "regular hexahedrons", or six-sided cubes.