Believe it or not, but they still exist: Atari computers and their users. A part of my software for Ataris and compatibles can be downloaded here. The sources for some of this software are available on GitHub: https://github.com/uweseimet/atari_public.
Commercial software for all Atari-compatible platforms
HDDRIVER, the versatile driver with tools for hard disk drives, removable media drives, memory cards and SSDs