In 1991, Linus Torvalds decided to share code that he had created for an operating system which would later become known as Linux, in the hope of getting feedback from others on how he could improve it. I came across the original email that Linus sent and was amazed by the modesty :

Hello everybody out there using minix -

I’m doing a (free) operating system (just a hobby, won’t be big and
professional like gnu) for 386(486) AT clones. This has been brewing
since april, and is starting to get ready. I’d like any feedback on
things people like/dislike in minix, as my OS resembles it somewhat
(same physical layout of the file-system (due to practical reasons)
among other things).

I’ve currently ported bash(1.08) and gcc(1.40), and things seem to work.
This implies that I’ll get something practical within a few months, and
I’d like to know what features most people would want. Any suggestions
are welcome, but I won’t promise I’ll implement them

Linus (torva…@kruuna.helsinki.fi)
PS. Yes – it’s free of any minix code, and it has a multi-threaded fs.
It is NOT protable (uses 386 task switching etc), and it probably never
will support anything other than AT-harddisks, as that’s all I have .

Note the modesty “just a hobby, won’t be big and professional like gnu“. Not even he new how big it would turn out. The full transcript of the responses are available here.