This Class M planet was generally uninhabited, with ancient ruins scattered across it's surface.

One of the largest areas of ruins is engulfed in a dimensional distortion that prevents transporter travel.  Inside this area is a high level of gamma radiation, and at it's centre a swirling vortex, which is in fact a dimensional portal.  The portal leads to a pocket dimension of high gamma radiation and is home to the Zaltael, the evolved remnants of the race that once lived on Betab.

Betab is also refufe for a small community of smugglers led by the Andorian, Wosata.

Episodes
"Yesterday's Voyage"

Star Trek appearances
n/a

This world was discovered by accident and was one of the few remain gin worlds of the ancient T'Kon Empire.  There was technology here from far off quadrants of the galaxy in a highly advance city.

Alas, the only remaining resident was a Borg Drone, who then attempted to assimilate the crew of the USS Firestar.  The Borg actions were stopped, but at the expense of all knowledge of the world and the vents that took place.

Kashaimae Tau

The planet Kashaimae Tau is within Klingon territory and just inside a Class II nebula, causing various technological disturbances. 

Kashaimae Tau was the location of a Klingon intelligence outpost.  The USS Firestar visited this world to gather intel on the Klingons, but the Klingons were not the only threat.  A Colossal electrical lifeform exists within a spacial rift within the nebula.