If we read the history of Calibre we will see that it was created for linux.
https://calibre-ebook.com/about#history
calibre started life on 31 October, 2006, soon after the release of the SONY PRS-500, the first e-ink based reader to be sold commercially in the US. At the time, I was a graduate student, with a lot of time on my hands. The PRS-500 did not work at all with Linux, my operating system of choice, so I decided to reverse engineer the USB protocol that it used, to get it working on Linux. This was accomplished with the help of the fine folks over at mobileread.com and calibre was born, albeit named libprs500.