Docker Engine (which is the core of what people think of as “Docker”) is FOSS. Docker Desktop (which most people rely on for local development) is free for individuals but I believe the license says companies over a certain size are required to pay.

And on top of that the paid plans also come with support, which large businesses frequently require, and private repositories on docker’s image repository.

Sqlite isn’t quite one person, but it is a very small team and is extremely widely used. https://www.sqlite.org/mostdeployed.html

Restic supports symlinks: https://restic.readthedocs.io/en/latest/040_backup.html#backing-up-special-items-and-metadata.