Components

This is a work-in progress description of which components could be used to put together the hello system.

Core OS

FreeBSD - Liberal license, great ZFS experience, slowly-changing, complete operating system system, no different competing distributions. Possible alternatives: NetBSD?
furybsd-livecd - Builds Live ISOs for FreeBSD, is customizable. Live system can be booted from ISO file using https://www.ventoy.net/ which allows one to have multiple Live ISOs in parallel. Live system optionally can be installed to disk. Current issues: Without Ventoy, copies the whole ISO to RAM before booting. Possible alternatives: NomadBSD, GhostBSD?

Qt 5 - Most cross-platform applications are written in it. Unlike Gtk, it is also not tied to Gnome.
lthemeengine - export QT_QPA_PLATFORMTHEME=lthemeengine to be able to get OK/Cancel buttons in the preferred order and to set custom colors for the Qt theme. Possible alternatives: Kvantum (allows themes to be made using SVG)

LxQt - Lightweight and based on Qt 5. Possible alternatives: Trident, Xfce (Gtk would bring in Gnome-related dependencies), KDE (would violate the "software minimalism" principle)

https://github.com/probonopd/filer/ - Very lightweight. Opinionated fork of PCManFM supporting AppDir. Can render the desktop, too. Current issues: Dependency on glib through libfm, limited Drag and Drop so far. Possible alternatives: https://github.com/probonopd/dfilemanager (more powerful, but does not build on FreeBSD yet)