If you had an Apple II, you had everything you needed to develop new software for it.
Looks like they used a Multics box at MIT. http://www.frankston.com/public/?name=ImplementingVisiCalc
Mobile phones and tablets have no such tools.
Their operating systems are shit packed on top of shit
Rather subjective. They do quite a bit more than Apple DOS or MS-DOS ever did.
fiddly little distraction machines that function as brightly colored noisy little pets
Same as it ever was:
a way to drain their parents' wallets by sending nonsense to each other 24 hours a day
Ever use a BBS back in the day?
the world-changing technology the PC made possible
The PC made computing accessible to commonfolk where it was previously the province of large institutions. Mobile continues this trend.
With the exception of FOSS, there hasn't been shit developed for any platform since.
We invented a new platform. Web Applications and APIs facilitated by cheap, commodity hardware have changed the nature of human communications and learning in the last 15 years.
distracted by Unity and HTML5 and Haskell and all the other flavors of proprietary dumbfuckery
Huh? None of those are proprietary. If a young person chose to learn about and use Haskell, I think they'd be well-equipped to learn quite a lot about how computers work.