DeRO-Juvenator! What the Heck is This???
 

Found with old roomate's stuff. In a paper bag marked "t.v. tube brightener," along with some other stuff.

Sounds like either a picture tube rejuvinator or a picture tube brightner. A brightner is a little device the plugs between the picture tube and the television circuitry, and boosts the filament voltage a bit to brighten an aging picture tube. (CRT's tend to get dim as they wear out). A picture tube rejuvinator would be a stand-alone device, and would plug into a picture tube, and be able to "zap" it to try to clear off the buildup on the cathode, once again in an attempt to brighten an aging tube. These fixes aren't permanent, and the brightners often times cause more problems than they solve, but they're good to keep a tube going, to squeeze a little bit of life out of it.

-Ian