A joint colony of Klingons, Romulans and the Federation.
Nimbus III is a planet that was intended to be a model of cooperation between the Federation, the Klingons and the Romulans, and which was known as the Planet of Galactic Peace. In practice it is a barren and dusty world, a failed experiment in which the three powers were unable to work together, and its settlement of Paradise City was shabby.
The planet was settled with the hope of building a better future, but a lack of resources and support left it in poverty. The settlers were mostly outcasts and others who had nowhere else to go, and the representatives of the three powers had little real authority, so that the planet was neglected.
Nimbus III is the setting of the early scenes of Star Trek V: The Final Frontier, in which Sybok takes the representatives hostage. Kirk, Spock and McCoy are sent to rescue the hostages, and they are captured by Sybok, who is Spock's half brother. He commandeers the Enterprise and takes it to the centre of the galaxy in search of God.