Atavachron

The atavachron was a time travel device from the planet Sarpeidon.

The device was capable of sending individuals back into the planet's past at any point. When James Kirk, Spock, and Leonard McCoy beamed down to Sarpeidon to investigate the lack of people on the planet, they were able to determine that, knowing their planet would be destroyed, Sarpeidon's inhabitants fled into the past. Kirk, Spock, and McCoy were accidentally transported through time by accident, but were recovered. 

Following the encounter, Commodore Antonio Delgado wanted to use the Guardian of Forever to study the atavachron's creation, but was unsuccessful.