It’s no secret that the Marvel Cinematic Universe is arguably the most successful film franchise running today. Each new Marvel movie is greeted with anticipation by fans, by and large receives a favorable critical response, and scores huge at the box office. But when The Avengers first grouped these disparate superheroes together in 2012, this was a somewhat novel idea (though admittedly not to comics fans who’d been reading crossover events for decades). This cinematic universe was something of a risky gamble, as general audiences were instead used to either direct sequels, spinoffs, or reboots—not disparate films with their own tones, characters, and themes taking place in the same universe as each other.

But as we all know that gamble paid off big time, and Hollywood went Cinematic Universe crazy. Studios began vying to launch their own interconnected series of films, but rather than making a slow-and-steady build to a crossover event like Marvel had, many of them tried to rush things to disappointing results. And in trying to do so much, so fast, with so little screentime, these overarching Cinematic Universe plans ended up getting scuttled.

So now seems a good time to jog our memories and look back on what could have been with these planned cinematic universes that never really got off the ground—with the caveat that some of these could still happen with a bit of retooling.