Re: ALGOL, PASCAL, MODULA 2, ADA
Unix wasn't sold as software, largely because the idea of software that could be installed, uninstalled, swapped, etc. didn't exist at the time. You bought a machine and it came with the necessary documentation, including the source code in order to be able to run it.
Unix became a standard, largely because of C, and as a result and some fairly large DARPA projects, the BSD effectively became the first software and it was both free to use and "open source", inasmuch as it was assumed you'd need the source code in order to fix any of the inevitable bugs.