A memory of the Linux days long gone.
I bought an ADSL modem that was a PCI card. Linux support was promised on the package.
The "Linux support" arrived in a .zip package. It had a Word document as instructions. At that point I had a bad feeling about it and I was right. They offered a precompiled kernel module for some ancient Redhat release. That's it.
I've since seen bad attempts at Linux support, but that modem still tops them all.