While we're plugging computer museums, I'll add the Media Archaeology Lab in Boulder, on the campus of the University of Colorado. It's no doubt a far smaller operation than most of the others mentioned here, but it has a lot of heart. Visitors are encouraged to hang out, play around with all the old computers and gadgets, peruse the floppy disk collection, and maybe find some games to play.

https://www.mediaarchaeologylab.com/