Girlfriends to Mork & Mindy

Dorian from Moesha appeared on episode of Girlfriends with Girlfriends' character Maya who later returned the favor and appeared in a episode of Moesha.

Hakeem and Niecy from Moesha went to the prom with Cher and Sean from Clueless.

Sabrina from Sabrina the Teenage Witch visited Cher from Clueless in the episode "Mr. Wright."

Sabrina the Teenage Witch also crossed over with Boy Meets World on several other occasions.

Boy Meets World and Step by Step both had episodes at Disney World and whiel in Disney World Eric from Boy Meets World met Dana from Step by Step.

The family from Step by Step was in the middle of a barbeque outside when Urkel from Family Matters came (literally) crashing in on the jetpack he had built on the last episode of Family Matters.

Family Matters was a spin-off of the character of Hariette and Carl Winslow from Perfect Strangers

Perfect Strangers' featured a game show segment in which the toilet was provided courtesy of Cunningham Hardware in Milwalkee, WI, owned by Howard Cunningham of Happy Days.

Mork's character originated from Happy Days