Star Trek is no stranger to crossovers. Characters from one series can and have popped up in another. There's an article in that, but this is not that article. Instead this about something much weirder: examples of crossovers with other shows from Webster, Here Come The Brides, seaQuest DSV, Buffy the Vampire Slayer, X-Men, Green Lantern and The Carol Burnett Show.
I wrote this about Star Trek's Oddest Crossovers.