[rskar]

>the company started out supplying a Fortran compiler for the Altair 8800

I would suppose maybe at some point they did (not sure on this) but it's long been my understanding that BASIC was their start.

Per https://en.wikipedia.org/wiki/Microsoft: Microsoft was founded by Paul Allen and Bill Gates on April 4, 1975, to develop and sell BASIC interpreters for the Altair 8800.

Per https://en.wikipedia.org/wiki/Altair_8800: The computer bus designed for the Altair was to become a de facto standard in the form of the S-100 bus, and the first programming language for the machine was Microsoft's founding product, Altair BASIC.

[qwertyuiop924]

And as we all know, Altair BASIC is the software about which "An Open Letter To Hobbyists" was written.