Diff'rent Strokes to Mannix

Hello Larry's Larry Alder crossed over onto Diff'rent Strokes for 3 different 2-part episodes

Hello Larry's characters were mentioned on Hi Honey, I'm Home!.

Alice & Trixie from The Honeymooners crossed over onto Hi Honey, I'm Home!

Here's Lucy's Lucy was driven around Miami by Ralph Cramden of The Hooneymooner's

Here's Lucy's Lucy Carter and Mannix's Mannix are held hostage in an episode of Here's Lucy.