Full House to The Suite LIfe of Zack and Cody

Steve Urkel visited Stephanie Tanner of Full House to convince her that glasses could be cool

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.

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.

Boy Meets World was continued decades later in Girl Meets World

Austin and Ally appear on an episode of Girl Meets World. Bringing the Disney Channel Live Action Universe into the Westphall Universe

Jessie and Austin & Ally crossed over

Mr. Moseby from The Suite Life was on Jessie