Goober and the Trucker's Paradise [pilot only] to Promised Land

Goober and the Trucker's Paradise was a failed spin off of Mayberry R.F.D. that instead ran as a one-shot special that had Goober Pyle running a truck stop.

was a spin off of The Andy Griffith Show

Gomer Pyle, U.S.M.C was a spin off of The Andy Griffith Show

The Lucy Show's Lucy Carmichael was accidentally drafted into Gomer Pyle, USMC's company on an episode of The Lucy Show.

Here's Lucy's Mary Jane Lewis was originally a character on The Lucy Show (also called The Lucille Ball Show).

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

Mannix returned to TV on an episode of Diagnosis Murder to solve an old unsolved case with the help of Dr Mark Sloan.

Promised Land's Russell Greene helped his boss Ryan Matthews face his families past, then Ryan crossed-over onto Diagnosis Murder to ID the body of one of his ex-wife's old friends