Software sold as a commodity, with a shrink wrap license, an idea pioneered by MicroSoft in 1975 with the release of MicrosoftBasic. 

CommoditySoftware was a true innovation (some say the only one BillGates was ever responsible for), and literally transformed the software industry within a decade. Before 1975, all software was either VendorSoftware, InHouseSoftware
or CustomizedSoftware, with much of the former two being distributed and used for free. The market for software was considered to be too small to support mass-produced software; furthermore, even similar systems had enough individual quirks, and different installations often needed it's particular software carefully tailored to it's particular uses. Even firms whose main business was a turnkey software suite would have it set up for the clients by consultants who would fit it to the specific systems. 

The advent of the MicroComputer changed this. The availability of mass-produced computers with minimal operating requirements (compared to a MiniComputer or a MainFrame) made it possible to write software that would write on hundreds of systems without customization, while the popularity of small systems with non-programmers gave such software a ready market. Even so, BillGates and PaulAllen showed considerable foresight in predicting that the Altair would lead to such a revolution, and in getting in literally at the first opening into the business. It is entirely conceivable that the history of computers would have been completely different had they not come up with the idea. On the one hand, the personal computer market would probably have foundered, or languished as a hobbyists' toy; on the other hand, the division between 'proprietary' and 'open' software might never have become as rancorous as it is today.
- JayOsako
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Larry Welke has a different version of history.  At http://www.softwarehistory.org/history/Welke1.html he says this about his InternationalComputerProgramsDirectory:

''"We estimated that in 1969 about 9% of the programs we listed were developed specifically as software products. By 1973, that number was up to 49%. And the idea of selling software as a product was no longer considered to be some kind of crazy, hair-brained scheme."''

-- EricHodges

''Thank you for the correction. I wasn't aware of this, and had been given the impression from the histories I'd read that selling software off-the-shelf was something new with MS Basic. However, I would be interested to know if the software Welke is referring to was truly turnkey (as in that it could be installed and run from the distribution by the end users), or if it included 'template' packages - that is, software that is written to a general design, then installed and tailored for the customer by consultants. I had the impression that most commercial software at the time was in that category, but that certainly could be a misunderstanding on my part. - JayOsako''