And that's if a proprietary compiler was actually available on the system. I worked for a widespread computational project that really needed GNU Fortran as eve

And that's if a proprietary compiler was actually available on the system. I worked for a widespread computational project that really needed GNU Fortran as eventually a reliable basis for people to use that was generally available. On the other hand, some bugs were common. There was at least one that originated in the original Unix f77 (which became f2c) that turned up in the Sun(?) compiler some time after it had been fixed in g77.