@pete_wright A project at work decided to use the terminal app ztop internally to monitor ZFS activity on Linux.
We realized that it was a FreeBSD-only program, and even though they both used ZFS, FreeBSD exposes statistics via sysctl, while Linux uses procfs.
The author had insufficient resources and/or interest to port it himself, so the porting fell to me.
I guess that makes ztop an example of (1), (2) _AND_ (3), where (3) is "PRs welcome"