Fro me, DESQview. Microsoft tried to buy it in order to use its tech in their windows system. I wonder how things would be today if they were able to purchase it. But DESQview said "no".
Instead it went into a slow death spiral due to Windows 95.
DESQview/X sucked the wind out of DESQview's sails. It was, on paper, a massive upgrade. I had been running DESQview for years, with a dial-up BBS in the background.
But you couldn't actually buy /X. After trying to buy a copy, my publisher even contacted DESQ's marketing people to get a copy for me, and they wouldn't turn one over. Supposedly there were some copies actually sold, but too few, too late, and then /X was dropped. There was at least one more release of plain DESQview after that, but by then Windows was eating its lunch.
Love seeing this one. My uncle was co-founder of Quarterdeck, and I grew up in a world of DESQview and QEMM. It was a big influence on me as a child.
Got a good family story about that whole acquisition attempt, but I don't want to speak publicly on behalf of my uncle. I know we've talked at length about the what-ifs of that moment.
I do have a scattering of some neat Quarterdeck memorabilia I can share, though:
https://www.dropbox.com/scl/fo/0ca1omn2kwda9op5go34e/ACpO6bz...