Three's Company, on ABC
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Well, I guess I used to watch this when I was a kid. Later on, after it had been off the air for some years, I kind of felt like it was stupid and felt guilty about having enjoyed it. But I was very young at the time, and didn't know any better. It was TV, and that was pretty much good enough. TV is good. Now... I don't know. I might consider watching reruns someday. Possibly. Maybe. But I doubt it. I suppose it may not have been quite as bad as I later thought. (In fact, it may have been a lot better than I later thought, though I still feel like there was too much humor based on sexual innuendo, for my taste.)
Anyway, the premise, as you well know, is that this guy named Jack Tripper (played by John Ritter) came to share an apartment with these two women, Janet Wood and Chrissy Snow. But even though they all had their own rooms, the landlord, Stanley Roper, didn't approve of a man sharing an apartment with women, so Jack had to pretend he was gay. What else to say? Um... Jack was a chef. And he had a friend named Larry Dallas (a stereotypical used car salesman). And at some point Chrissy moved out, and was replaced by her cousin Cindy, who was later replaced by someone named Terri. Oh, and Mr. Roper had a wife named Helen, with whom he argued a lot. Eventually the Ropers were replaced by a new landlord, Mr. Furley, who was played by Don Knotts (of Andy Griffith Show fame). But Jack still had to go on pretending to be gay. Dunno what else to say. Except the theme song was pretty memorable.
Three's a Crowd, on ABC
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This was a short-lived spin-off, in which Jack moved out of the apartment and in with his girlfriend, Vicky. Her father didn't like that they were living together, so he made some trouble for them. But I don't remember the show that well. I seem to recall liking it, at the time, though.
There was also a "Three's Company" spin-off called The Ropers, but I don't think I ever saw that.