A primitive form of space age transportation. They are a precursor to Gravity/Warp Drives. They are also called Tachyon Drives, and Hyperwave Drives.
Mass Drive, effectively uses tachyon-graviton waves to send a ship flying past the speed of light. It is essentially an electromagnetic field, working upon the mass of the ship and everything inside with the gravity wave generators. Due to the nature of the system, occupants inside must be placed in Hypersleep to avoid aging to death.
It is this feature that causes the internal structure of the ship to use more archaic forms of technology, such as CRT Tubes as opposed to flatscreen monitors and hologram projectors, due to them being (at that point in the species' development) easier to make more long lasting as the wave generated by the drive places strain on everything inside of it.
Commonly, the most common and most basic method of FTL in most galaxies is the Warp Drive. The Mass Drive, is the general precursor and primitive cousin to the Warp Drive. The Mass Drive is typically used by primitive species, yet is often used centuries into space exploration due to a refusal to upgrade, often due to various reasons.
In such cases, the Mass Drive is often abandoned after a race's first interstellar/species war, providing they survive it.
Mass Gates are often used in tandem to increase the speed between already discovered systems.