The September Open Thread, Part 2 has got nearly 800 posts, so let's have a little breathing room.
This thread is for the discussion of Less Wrong topics that have not appeared in recent posts. If a discussion gets unwieldy, celebrate by turning it into a top-level post.
To clarify the question a bit, I would consider dividing software technologies into three categories:
Technologies developed while the necessary computing resources were still unavailable or too expensive, which flourished later when the resources became cheap enough. For example, Alan Turing famously devised a chess program which he could only run using paper and pencil.
Technologies that appeared very soon after the necessary computing resources became available and cheap enough, suggesting that the basic idea was fairly straightforward after all, and it was only necessary to give smart people some palpable incentive to think about it. Examples such as the first browsers and spreadsheets would be in this category.
Technologies for which the necessary computing resources had been cheaply available for a long time before someone finally came up with them, suggesting an extraordinary intellectual breakthrough. I cannot think of any such examples, and it doesn't seem like anyone else in this thread can either.
This reinforces my cynical view of software technologies in general, namely that their entire progress in the last few decades has been embarrassingly limited considering the amount of intellectual power poured into them.
Here's an interesting related thought experiment that reinforces my cynicism further. Suppose that some miraculous breakthrough in 1970 enabled the production of computers equally cheap, powerful, compact, and easily networked as we have today. What do we have today in terms of software technology that the inhabitants of this hypothetical world wouldn't have by 1980?
Chess had steady algorithmic improvements on the same order as the gains from hardware: Deep Fritz and Rybka both got to better performance per FLOP than Deep Blue, etc. More generally, I think that looking at quantitative metrics (as opposed to whole new capabilities) like game performance, face recognition, image processing, etc, will often give you independent hardware and software components to growth.